Condorcet Attack Against Fair Transaction Ordering

We introduce the Condorcet attack, a new threat to fair transaction ordering. Specifically, the attack undermines batch-order-fairness, the strongest notion of transaction fair ordering proposed to date. The batch-order-fairness guarantees that a transaction tx is ordered before tx' if a majority of nodes in the system receive tx before tx'; the only exception (due to an impossibility result) is when tx and tx' fall into a so-called "Condorcet cycle". When this happens, tx and tx' along with other transactions within the cycle are placed in a batch, and any unfairness inside a batch is ignored. In the Condorcet attack, an adversary attempts to undermine the system's fairness by imposing Condorcet cycles to the system. In this work, we show that the adversary can indeed impose a Condorcet cycle by submitting as few as two otherwise legitimate transactions to the system. Remarkably, the adversary (e.g., a malicious client) can achieve this even when all the nodes in the system behave honestly. A notable feature of the attack is that it is capable of "trapping" transactions that do not naturally fall inside a cycle, i.e. those that are transmitted at significantly different times (with respect to the network latency). To mitigate the attack, we propose three methods based on three different complementary approaches. We show the effectiveness of the proposed mitigation methods through simulations, and explain their limitations

A continuous morphological approach to study the evolution of pollen in a phylogenetic context: An example with the order Myrtales

The study of pollen morphology has historically allowed evolutionary biologists to assess phylogenetic relationships among Angiosperms, as well as to better understand the fossil record. During this process, pollen has mainly been studied by discretizing some of its main characteristics such as size, shape, and exine ornamentation. One large plant clade in which pollen has been used this way for phylogenetic inference and character mapping is the order Myrtales, composed by the small families Alzateaceae, Crypteroniaceae, and Penaeaceae (collectively the “CAP clade”), as well as the large families Combretaceae, Lythraceae, Melastomataceae, Myrtaceae, Onagraceae and Vochysiaceae. In this study, we present a novel way to study pollen evolution by using quantitative size and shape variables. We use morphometric and morphospace methods to evaluate pollen change in the order Myrtales using a time-calibrated, supermatrix phylogeny. We then test for conservatism, divergence, and morphological convergence of pollen and for correlation between the latitudinal gradient and pollen size and shape. To obtain an estimate of shape, Myrtales pollen images were extracted from the literature, and their outlines analyzed using elliptic Fourier methods. Shape and size variables were then analyzed in a phylogenetic framework under an Ornstein-Uhlenbeck process to test for shifts in size and shape during the evolutionary history of Myrtales. Few shifts in Myrtales pollen morphology were found which indicates morphological conservatism. Heterocolpate, small pollen is ancestral with largest pollen in Onagraceae. Convergent shifts in shape but not size occurred in Myrtaceae and Onagraceae and are correlated to shifts in latitude and biogeography. A quantitative approach was applied for the first time to examine pollen evolution across a large time scale. Using phylogenetic based morphometrics and an OU process, hypotheses of pollen size and shape were tested across Myrtales. Convergent pollen shifts and position in the latitudinal gradient support the selective role of harmomegathy, the mechanism by which pollen grains accommodate their volume in response to water loss

Kriebel_Khabbazian_Sytsma_2017

This data package includes the files needed to reproduce the analyses of the following paper: Kriebel, R., Khabbazian, M., and K. J. Sytsma. A continuous morphological approach to study the evolution of pollen in a phylogenetic context: an example with the order Myrtale

Ist Wettbewerb geeignet, das Leistungsangebot oeffentlicher Einrichtungen zu verbessern?: Projektbericht

Available from Bibliothek des Instituts fuer Weltwirtschaft, ZBW, Duesternbrook Weg 120, D-24105 Kiel C 148156 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Morphospaces of pollen shape in Myrtales grouped by family.

<p>Morphospaces of pollen shape in Myrtales grouped by family. The families Alzateaceae, Crypteroniaceae, and Penaeaceae are collectively included under the “CAP clade”. A: Empirical morphospace of pollen shape variation in equatorial view. B: Theoretical morphospace of pollen shape variation in equatorial view. C: Empirical morphospace of pollen shape variation in polar view. D: Theoretical morphospace of pollen shape variation in polar view.</p

Optimal Phase Control for Equal-Gain Transmission in MIMO Systems With Scalar Quantization: Complexity and Algorithms

The complexity of the optimal phase control problem in wireless MIMO systems with scalar feedback quantization and equal-gain transmission is studied. The problem is shown to be NP-hard when the number of receive antennas grows linearly with the number of transmit antennas. For the case where the number of receive antennas is constant, the problem can be solved in polynomial time. An optimal algorithm is explicitly constructed. For practical purposes, a low-complexity algorithm based on local search is presented. Simulation results show that its performance is nearly optimal

Phylogenetic generalized least squares (PGLS) regression models of pollen traits.

<p>**, <0.005; ***, <0.001.</p

Phylogenetic generalized least squares (PGLS) regression models of pollen traits and absolute latitude.

<p>***, <0.001.</p

Examples of pollen grains in Myrtales.

<p>Scanning electron micrographs of pollen grains from selected species of Myrtales. Representing the CAP clade is <i>Saltera sarcocolla</i>; <i>Bucida macrostachya</i> in equatorial view and <i>Conocarpus erecta</i> in polar view (Combretaceae); <i>Heimia salicifolia</i> (Lythraceae); <i>Miconia alypifolia</i> in equatorial view and <i>Miconia caesia</i> in polar view for (Melastomaceae); <i>Tristania conferta</i> (Myrtaceae); <i>Calylophus toumeyi</i> (Onagraceae). Scale bars are 5 um except for Onagraceae which is 50 <i>um</i>. Adapted from [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0187228#pone.0187228.ref050" target="_blank">50</a>] with permission from the Annals of the Missouri Botanical Garden Press.</p