Proof of Luck: an Efficient Blockchain Consensus Protocol

In the paper, we present designs for multiple blockchain consensus primitives and a novel blockchain system, all based on the use of trusted execution environments (TEEs), such as Intel SGX-enabled CPUs. First, we show how using TEEs for existing proof of work schemes can make mining equitably distributed by preventing the use of ASICs. Next, we extend the design with proof of time and proof of ownership consensus primitives to make mining energy- and time-efficient. Further improving on these designs, we present a blockchain using a proof of luck consensus protocol. Our proof of luck blockchain uses a TEE platform's random number generation to choose a consensus leader, which offers low-latency transaction validation, deterministic confirmation time, negligible energy consumption, and equitably distributed mining. Lastly, we discuss a potential protection against up to a constant number of compromised TEEs.Comment: SysTEX '16, December 12-16, 2016, Trento, Ital

Ignition and Front Propagation in Polymer Electrolyte Membrane Fuel Cells

Water produced in a Polymer Electrolyte Membrane (PEM) fuel cell enhances membrane proton conductivity; this positive feedback loop can lead to current ignition. Using a segmented anode fuel cell we study the effect of gas phase convection and membrane diffusion of water on the spatiotemporal nonlinear dynamics - localized ignition and front propagation - in the cell. Co-current gas flow causes ignition at the cell outlet, and membrane diffusion causes the front to slowly propagate to the inlet; counter-current flow causes ignition in the interior of the cell, with the fronts subsequently spreading towards both inlets. These instabilities critically affect fuel cell performance

Causes of the Violation of Integrity Constraints for Supporting the Quality of Databases

[EN] The quality of the information provided by databases can be captured by integrity constraints. Thus, violated cases of constraints may serve as a basis for measuring the quality of given database states. A quality metric with the potential of more accuracy is obtained by measuring the causes, i.e., data that are responsible for constraint violations. Such measures also serve for controlling quality impairment across updates.Partially supported by FEDER and the Spanish grants TIN2009-14460-C03 and TIN2010-17139Decker, H. (2011). Causes of the Violation of Integrity Constraints for Supporting the Quality of Databases. Lecture Notes in Computer Science. 6786:283-292. https://doi.org/10.1007/978-3-642-21934-4_24S2832926786Ceri, S., Gottlob, G., Tanca, L.: What you always wanted to know about Datalog (and never dared to ask). TKDE 1(1), 146–166 (1989)Christiansen, H., Martinenghi, D.: On simplification of database integrity constraints. Fundam. Inform. 71(4), 371–417 (2006)Decker, H.: Answers that Have Integrity in Databases that Violate Constraints. Presented at the ICALP Workshop SDKB 2010, to appear in the Post-Workshop Proceedings of SDKB (2011)Decker, H.: Toward a uniform cause-based approach to inconsistency-tolerant database semantics. In: Meersman, R., Dillon, T., Herrero, P. (eds.) OTM 2010. LNCS, vol. 6427, pp. 983–998. Springer, Heidelberg (2010)Decker, H.: Quantifying the Quality of Stored Data by Measuring their Integrity. In: Proc. DIWT 2009, Workshop SMM, pp. 823–828. IEEE, Los Alamitos (2009)Decker, H., Martinenghi, D.: Inconsistency-tolerant Integrity Checking. TKDE 23(2), 218–234 (2011)Decker, H., Martinenghi, D.: Modeling, measuring and monitoring the quality of information. In: Heuser, C.A., Pernul, G. (eds.) ER 2009. LNCS, vol. 5833, pp. 212–221. Springer, Heidelberg (2009)Grant, J., Hunter, A.: Measuring inconsistency in knowledgebases. J. Intelligent Information Systems 27(2), 159–184 (2006)Ramakrishnan, R., Gehrke, J.: Database Management Systems. McGraw-Hill, New York (2003

On the Development of the Artillery Flight Characterization Electronics Rescue Kit

21st AIAA Aerodynamic Decelerator Systems Technology Conference and Seminar, 23 - 26 May 2011, Dublin, IrelandThis paper investigates a prospective avionics suite rescue kit to salvage some of the state-of-the-art electronics in the data-collecting fuze system employed on an artillery projectile. A single-use data collection fuze is currently in use by the Army that relays sensor measurements for the purpose of characterizing the flight of an artillery projectile. The goal of the present study is to develop a parachute/parafoil-based system to be deployed automatically at apogee, so that the ! Reuse-Fuze" becomes separated from the body of the artillery shell and safely recovered. The paper presents the overall design of the Reuse-Fuze system, including the release mechanism, deceleration system, and impact survivability considerations. The successful design of a recoverable and reusable fuze-shaped data collection system will allow the Army to conduct repeated artillery testing without increasing the cost of expensive electronics hardware

Kinetic modelling of runaway electron avalanches in tokamak plasmas

Runaway electrons (REs) can be generated in tokamak plasmas if the accelerating force from the toroidal electric field exceeds the collisional drag force due to Coulomb collisions with the background plasma. In ITER, disruptions are expected to generate REs mainly through knock-on collisions, where enough momentum can be transferred from existing runaways to slow electrons to transport the latter beyond a critical momentum, setting off an avalanche of REs. Since knock-on runaways are usually scattered off with a significant perpendicular component of the momentum with respect to the local magnetic field direction, these particles are highly magnetized. Consequently, the momentum dynamics require a full 3-D kinetic description, since these electrons are highly sensitive to the magnetic non-uniformity of a toroidal configuration. A bounce-averaged knock-on source term is derived. The generation of REs from the combined effect of Dreicer mechanism and knock-on collision process is studied with the code LUKE, a solver of the 3-D linearized bounce-averaged relativistic electron Fokker-Planck equation, through the calculation of the response of the electron distribution function to a constant parallel electric field. This work shows that the avalanche effect can be important even in non-disruptive scenarios. RE formation through knock-on collisions is found to be strongly reduced when taking place off the magnetic axis, since trapped electrons cannot contribute to the RE population. The relative importance of the avalanche mechanism is investigated as a function of the key parameters for RE formation; the plasma temperature and the electric field strength. In agreement with theoretical predictions, the simulations show that in low temperature and E-field knock-on collisions are the dominant source of REs and can play a significant role for RE generation, including in non-disruptive scenarios.Comment: 23 pages, 12 figure

Radiative Tau Decays with One Pseudoscalar Meson

We have calculated the decay $\tau \rightarrow \nu \pi(K) \gamma$. We present the photon energy spectrum, the meson-photon invariant mass spectrum and the integrated rate as a function of a photon energy cut or an invariant mass cut. Both the internal bremsstrahlung and the structure dependent radiation have been taken into account. To this aim we have parametrized the form factors $F_V$ and $F_A$, which determine the structure dependent radiation. Observables especially suited for the measurement of the structure dependent form factors are found and implications on the width of the $a_1$ discussed.Comment: p.20, TTP93-1, LaTe