Fission modes of 256Fm and 258Fm in a microscopic approach

A static microscopic study of potential-energy surfaces within the Skyrme-Hartree-Fock-plus-BCS model is carried out for the 256Fm and 258Fm isotopes with the goal of deducing some properties of spontaneous fission. The calculated fission modes are found to be in agreement with the experimentaly observed asymmetric-to-symmetric transition in the fragment-mass distributions and with the high- and low-total-kinetic-energy modes experimentally observed in 258Fm. Most of the results are similar to those obtained in macroscopic-microscopic models as well as in recent Hartree-Fock-Bogolyubov calculations with the Gogny interaction, with a few differences in their interpretations. In particular an alternative explanation is proposed for the low-energy fission mode of 258Fm.Comment: 14 pages, 11 figures, 3 tables, submitted to Phys. Rev.

Nonpartisan election formats do not affect voting behaviors

Nonpartisan elections—in which candidates are not endorsed by a political party and their party affiliation does not appear on the ballot—have been criticized as depriving crucial information to voters, making it difficult for them to vote for candidates that represent their beliefs. Chris W. Bonneau and Damon M. Cann tested the impact of nonpartisan election conditions using both a laboratory experiment and data from the Cooperative Congressional Election Survey. They find that there is no significant difference between voting behaviors in partisan and nonpartisan election formats

Vacuum Polarization Effects in the Lorentz and PCT Violating Electrodynamics

In this work we report new results concerning the question of dynamical mass generation in the Lorentz and PCT violating quantum electrodynamics. A one loop calculation for the vacuum polarization tensor is presented. The electron propagator, "dressed" by a Lorentz breaking extra term in the fermion Lagrangian density, is approximated by its first order: this scheme is shown to break gauge invariance. Then we rather consider a full calculation to second order in the Lorentz breaking parameter: we recover gauge invariance and use the Schwinger-Dyson equation to discuss the full photon propagator. This allows a discussion on a possible photon mass shift as well as measurable, observable physical consequences, such as the Lamb-shift.Comment: Latex file, 19 pages, no figures, includes PACS number

An oscillator circuit to produce a radio-frequency discharge and application to metastable helium saturated absorption spectroscopy

We present an rf gas discharge apparatus which provides an atomic frequency reference for laser manipulation of metastable helium. We discuss the biasing and operation of a Colpitts oscillator in which the discharge coil is part of the oscillator circuit. Radiofrequency radiation is reduced by placing the entire oscillator in a metal enclosure.Comment: 9 pages, 5 figure

Développement du système racinaire du cocotier en fonction du milieu en Côte d'Ivoire

La densité du système racinaire du cocotier a été estimée par la Station Marc-Delorme (Côte d'Ivoire) grâce à des prélèvements de cylindres de sol, à partir desquels ont été calculés des poids secs de racines par unité de volume de sol. Pour une même situation, les résultats obtenus avec les deux outils utilisés, pala-draga et tarière hollandaise, ne sont pas comparables. Le système racinaire du cocotier présente une variabilité intervariétale, et il s'adapte aux différentes conditions de milieu rencontrées : texture du sol, présence éventuelle d'un horizon induré, conditions d'humidité, niveau de fertilisation. La production d'une cocoteraie n'est pourtant pas liée de manière obligatoire à la densité de son réseau racinaire, d'où l'intérêt de s'intéresser également au fonctionnement des racine

GOTCHA Password Hackers!

We introduce GOTCHAs (Generating panOptic Turing Tests to Tell Computers and Humans Apart) as a way of preventing automated offline dictionary attacks against user selected passwords. A GOTCHA is a randomized puzzle generation protocol, which involves interaction between a computer and a human. Informally, a GOTCHA should satisfy two key properties: (1) The puzzles are easy for the human to solve. (2) The puzzles are hard for a computer to solve even if it has the random bits used by the computer to generate the final puzzle --- unlike a CAPTCHA. Our main theorem demonstrates that GOTCHAs can be used to mitigate the threat of offline dictionary attacks against passwords by ensuring that a password cracker must receive constant feedback from a human being while mounting an attack. Finally, we provide a candidate construction of GOTCHAs based on Inkblot images. Our construction relies on the usability assumption that users can recognize the phrases that they originally used to describe each Inkblot image --- a much weaker usability assumption than previous password systems based on Inkblots which required users to recall their phrase exactly. We conduct a user study to evaluate the usability of our GOTCHA construction. We also generate a GOTCHA challenge where we encourage artificial intelligence and security researchers to try to crack several passwords protected with our scheme.Comment: 2013 ACM Workshop on Artificial Intelligence and Security (AISec

Constrained Cost-Coupled Stochastic Games with Independent State Processes

We consider a non-cooperative constrained stochastic games with N players with the following special structure. With each player there is an associated controlled Markov chain. The transition probabilities of the i-th Markov chain depend only on the state and actions of controller i. The information structure that we consider is such that each player knows the state of its own MDP and its own actions. It does not know the states of, and the actions taken by other players. Finally, each player wishes to minimize a time-average cost function, and has constraints over other time-avrage cost functions. Both the cost that is minimized as well as those defining the constraints depend on the state and actions of all players. We study in this paper the existence of a Nash equilirium. Examples in power control in wireless communications are given.Comment: 7 pages, submitted in september 2006 to Operations Research Letter

Restauration de la fertilité des sols lors de la replantation d'une cocoteraie

La prolongation de deux expériences, déjà décrites dans un article précédent, a prouvé que dans le cas de vieilles cocoteraies établies sur sables quaternaires dans le Sud-Est de la Côte d'Ivoire, et mal gérées, une régénération de sol par une légumineuse améliorante était indispensable en replantation. Sur ces sols très pauvres, parmi 7 légumineuses rampantes testées, aucune n'a pu être adaptée. De bons résultats ont par contre été obtenus avec 3 légumineuses arborescentes, Albizia falcata, Acacia mangium et Acacia auriculiformis. Une véritable association cocotier-légumineuse arborescente est maintenant envisagée, permettant de restaurer la fertilité du sol et de produire à la fois des noix de coco et du bois de feu. En Afrique de l'Ouest, ce type d'association intéresse les cocoteraies de toute la bande côtière de la Côte d'Ivoire au Nigeri