Dirac point metamorphosis from third-neighbor couplings in graphene

We study the band structure and the density of states of graphene in the presence of a next-to-nearest-neighbor coupling (N2) and a third-nearest-neighbor coupling (N3). We show that for values of N3 larger or equal to 1/3 of the value of the nearest-neighbor hopping (NN), extra Dirac points appear in the spectrum. If N3 is exactly equal to 1/3 NN, the new Dirac points are localized at the M points of the Brillouin zone and are hybrid: the electrons have a linear dispersion along the GammaM direction and a quadratic dispersion along the perpendicular direction MK. For larger values of N3 the new points have a linear dispersion, and are situated along the MK line. For a value of N3 equal to 1/2 NN, these points merge with the Dirac cones at the K points, yielding a gapless quadratic dispersion around K, while for larger values each quadratic point at K splits again into four Dirac points. The effects of changing the N2 coupling are not so dramatic. We calculate the density of states and we show that increasing the N3 coupling lowers the energy of the Van Hove singularities, and when N3 is larger than 1/3 NN the Van Hove singularities split in two, giving rise to extra singularities at low energies.Comment: 13 pages, 10 figure

Systemization of Pluggable Transports for Censorship Resistance

An increasing number of countries implement Internet censorship at different scales and for a variety of reasons. In particular, the link between the censored client and entry point to the uncensored network is a frequent target of censorship due to the ease with which a nation-state censor can control it. A number of censorship resistance systems have been developed thus far to help circumvent blocking on this link, which we refer to as link circumvention systems (LCs). The variety and profusion of attack vectors available to a censor has led to an arms race, leading to a dramatic speed of evolution of LCs. Despite their inherent complexity and the breadth of work in this area, there is no systematic way to evaluate link circumvention systems and compare them against each other. In this paper, we (i) sketch an attack model to comprehensively explore a censor's capabilities, (ii) present an abstract model of a LC, a system that helps a censored client communicate with a server over the Internet while resisting censorship, (iii) describe an evaluation stack that underscores a layered approach to evaluate LCs, and (iv) systemize and evaluate existing censorship resistance systems that provide link circumvention. We highlight open challenges in the evaluation and development of LCs and discuss possible mitigations.Comment: Content from this paper was published in Proceedings on Privacy Enhancing Technologies (PoPETS), Volume 2016, Issue 4 (July 2016) as "SoK: Making Sense of Censorship Resistance Systems" by Sheharbano Khattak, Tariq Elahi, Laurent Simon, Colleen M. Swanson, Steven J. Murdoch and Ian Goldberg (DOI 10.1515/popets-2016-0028

Large permeabilities of hourglass nanopores: From hydrodynamics to single file transport

In fluid transport across nanopores, there is a fundamental dissipation that arises from the connection between the pore and the macroscopic reservoirs. This entrance effect can hinder the whole transport in certain situations, for short pores and/or highly slipping channels. In this paper, we explore the hydrodynamic permeability of hourglass shape nanopores using molecular dynamics (MD) simulations, with the central pore size ranging from several nanometers down to a few Angstr{\"o}ms. Surprisingly, we find a very good agreement between MD results and continuum hydrodynamic predictions, even for the smallest systems undergoing single file transport of water. An optimum of permeability is found for an opening angle around 5 degree, in agreement with continuum predictions, yielding a permeability five times larger than for a straight nanotube. Moreover, we find that the permeability of hourglass shape nanopores is even larger than single nanopores pierced in a molecular thin graphene sheet. This suggests that designing the geometry of nanopores may help considerably increasing the macroscopic permeability of membranes

Dissimilarity-based representation for radiomics applications

Radiomics is a term which refers to the analysis of the large amount of quantitative tumor features extracted from medical images to find useful predictive, diagnostic or prognostic information. Many recent studies have proved that radiomics can offer a lot of useful information that physicians cannot extract from the medical images and can be associated with other information like gene or protein data. However, most of the classification studies in radiomics report the use of feature selection methods without identifying the machine learning challenges behind radiomics. In this paper, we first show that the radiomics problem should be viewed as an high dimensional, low sample size, multi view learning problem, then we compare different solutions proposed in multi view learning for classifying radiomics data. Our experiments, conducted on several real world multi view datasets, show that the intermediate integration methods work significantly better than filter and embedded feature selection methods commonly used in radiomics.Comment: conference, 6 pages, 2 figure

Laser Doppler Velocimetry for Joint Measurements of Acoustic and Mean Flow Velocities : LMS-based Algorithm and CRB Calculation

This paper presents a least mean square (LMS) algorithm for the joint estimation of acoustic and mean flow velocities from laser doppler velocimetry (LDV) measurements. The usual algorithms used for measuring with LDV purely acoustic velocity or mean flow velocity may not be used when the acoustic field is disturbed by a mean flow component. The LMS-based algorithm allows accurate estimations of both acoustic and mean flow velocities. The Cram\'er-Rao bound (CRB) of the associated problem is determined. The variance of the estimators of both acoustic and mean flow velocities is also given. Simulation results of this algorithm are compared with the CRB and the comparison leads to validate this estimator

Underground, upperground et middle-ground : les collectifs créatifs et la capacité créative de la ville

Cet article analyse un acteur méconnu des villes créatives : les collectifs créatifs. Les villes créatives s’articulent selon trois strates actives. Les firmes – upperground - absorbent les connaissances émergeant des activités créatives de la ville alors que les acteurs de l’underground explorent et proposent de nouvelles avenues créatives. Dans ce contexte, les collectifs créatifs du middleground assument une fonction d’intégration des connaissances et de transfert entre l’underground et l’upperground. À travers quelques exemples empiriques, la nature et les rôles de ces collectifs sont discutés, ainsi que les différents modes de relations qu’ils pourraient développer avec les firmes et leurs milieux.In this paper, we analyze an unrecognized actor of the creative cities: creative collectives. We identify three active layers in the creative cities. Firms – the upperground – absorb knowledge emerging from the creative activities in the city whereas actors from the underground explore and suggest new creative ways. In this context, creative collectives from the middleground play a role of knowledge integration and transfer between the underground and the upperground. Through some empirical examples, we assess the nature and roles of those collectives, and discuss the various relationships they could develop with firms and their milieu.Este artículo analiza a un actor desconocido de las ciudades creativas: los colectivos creativos. Las ciudades creativas se articulan según tres estratos activos. Las empresas - upperground - absorben los conocimientos que emergen de actividades creativas de la ciudad mientras los actores del underground exploren y propongan de nuevas avenidas creativas. En este contexto, los colectivos creativos del middleground asumen una función de integración de conocimientos y transferencia entre el underground y el upperground. A través de algunos ejemplos empíricos, la naturaleza y los papeles de estos colectivos son discutidos, así como los diferentes modos de relaciones que podrían desarrollar con las empresas y sus medios

De la biodiversité à la diversité : les biodiversités au regard des territoires

International audienceBiodiversity has become a subject of major interest since twenty years, giving rise to scientifc works, international conferences and discussions. Fears concerning the decline of life diversity take a strong place in the current environmental stakes. Without denying the reasons that justify such a concern, this paper focuse on the territorial aspects of the topic. The naturalist approach seems partly inadequate to deal with the matter in a spatial and temporal point of view. Taking in account “natural” and social areas enable to demonstrate the relativity of the matter and the diversity of cases. This paper consider biodiversity partly as a result of social history and thus, as a temporal process with period of decline alternating with period of expansion.La biodiversité suscite depuis vingt ans travaux scientifiques, réunions internationales et débats. Les craintes relatives à l'érosion accélérée de la diversité du vivant sont au cœur des enjeux environnementaux actuels. Sans nier les raisons qui justifient une légitime préoccupation, cet article vise à intégrer la dimension territoriale d'un problème trop souvent conçu sous l'angle de la seule écologie. Or l'approche purement naturaliste nous semble insuffisante pour aborder la biodiversité dans une perspective spatiale et temporelle pertinente. La prise en compte des territoires, « naturels » et sociaux, permet de montrer la contingence d'une notion et la diversité des réalités qui se cachent sous une notion trop souvent utilisée au singulier. Considérée comme un aspect du territoire, la problématique de la biodiversité évolue. Elle intègre alors les aléas historiques propres à toute diversité qui se crée, se développe et disparaît. Faut-il et peut-on alors protéger la biodiversité

Two-dimensional transport analysis of transdermal drug absorption with a non-perfect sink boundary condition at the skin-capillary interface

A transient percutaneous drug absorption model was solved in two dimensions. Clearance of the topically-applied pharmaceutical occured at the skin-capillary boundary. Timolol penetration profiles in the dermal tissue were produced revealing concentration gradients in the directions normal and parallel to the skin surface. Ninety-eight percent of the steady-state flux was reached after 85. h or four time constants. The analytical solution procedure agreed with published results. As the clearance rate increased relative to diffusion, the delivery rate and amount of drug absorbed into the bloodstream increased while the time to reach the equilibrium flux decreased. Researchers can apply the closed-form expressions to simulate the process, estimate key parameters and design devices that meet specific performance requirements. © 2013 Elsevier Inc