Perfectly secure data aggregation via shifted projections

We study a general scenario where confidential information is distributed among a group of agents who wish to share it in such a way that the data becomes common knowledge among them but an eavesdropper intercepting their communications would be unable to obtain any of said data. The information is modelled as a deck of cards dealt among the agents, so that after the information is exchanged, all of the communicating agents must know the entire deal, but the eavesdropper must remain ignorant about who holds each card. Valentin Goranko and the author previously set up this scenario as the secure aggregation of distributed information problem and constructed weakly safe protocols, where given any card $c$, the eavesdropper does not know with certainty which agent holds $c$. Here we present a perfectly safe protocol, which does not alter the eavesdropper's perceived probability that any given agent holds $c$. In our protocol, one of the communicating agents holds a larger portion of the cards than the rest, but we show how for infinitely many values of $a$, the number of cards may be chosen so that each of the $m$ agents holds more than $a$ cards and less than $2m^2a$

The evolution of a climate regime: Kyoto to Marrakech

Abstract in HTML and technical report in PDF available on the Massachusetts Institute of Technology Joint Program on the Science and Policy of Global Change Website. (http://mit.edu/globalchange/www/)Includes bibliographical references (p. 16-17).At meetings in Bonn and Marrakech in 2001, the Conference of the Parties to the Framework Convention on Climate Change broke through an impasse on the detailed provisions needed to allow the Kyoto Protocol to enter into force. Key ingredients in the breakthrough included U.S. withdrawal from the process, an effective relaxation of emissions targets for Japan, Canada, and Russia, and provision of access to unrestricted emissions trading. We analyze the costs of implementation and the environmental effectiveness of the Bonn-Marrakech agreement, and its effect on the relative roles of CO₂ vs. non-CO₂ greenhouse gases. The ability of the major sellers of permits, notably Russia and Ukraine, to restrict access to permits, and the ability to trade across all greenhouse gases controlled under the Protocol, are both found to have a significant effect for both costs and effectiveness. Finally, the implications of the agreement for the future evolution of the climate regime are explored

Planetary Nebulae Kinematics in M31

We present kinematics of 135 planetary nebulae in M31 from a survey covering 3.9 square degrees and extending out to 15 kpc from the southwest major axis and more than 20 kpc along the minor axis. The majority of our sample, even well outside the disk, shows significant rotational support (mean line-of-sight velocity 116 km/s). We argue that these PN belong to the outer part of M31's large de Vaucouleurs bulge. Only five PN have velocities clearly inconsistent with this fast rotating bulge. All five may belong to tidal streams in M31's outer halo. One is projected on the Northern Spur, and is counter-rotating with respect to the disk there. Two are projected along the major axis at X=-10 kpc and have M32-like velocities; they could be debris from that galaxy. The remaining two halo PN are located near the center of the galaxy and their velocities follow the gradient found by Ibata et al. (2004), implying that these PN could belong to the Southern Stream. If M31 has a non-rotating, pressure-supported halo, we have yet to find it, and it must be a very minor component of the galaxy.Comment: accepted to ApJ; main body of paper is 36 pages, including 14 figure

Extraction of Scores and Average From Algerian High-School Degree Transcripts

A system for extracting scores and average from Algerian High School Degree Transcripts is proposed. The system extracts the scores and the average based on the localization of the tables gathering this information and it consists of several stages. After preprocessing, the system locates the tables using ruling-lines information as well as other text information. Therefore, the adopted localization approach can work even in the absence of certain ruling-lines or the erasure and discontinuity of lines. After that, the localized tables are segmented into columns and the columns into information cells. Finally, cells labeling is done based on the prior knowledge of the tables structure allowing to identify the scores and the average. Experiments have been conducted on a local dataset in order to evaluate the performances of our system and compare it with three public systems at three levels, and the obtained results show the effectiveness of our system