Demand Uncertainty and Airline Network Morphology with Strategic Interactions

In this paper, we examine how strategic interactions affect airline network. We develop a three stage duopoly game: at stage 1 airlines determines their network structure (linear versus hub-and-spoke). At stage 2 they decide on their capacities, and at stage 3 firms compete in quantities. The main feature of the model is that firms have to decide on network structure and capacities while facing demand uncertainty. We show that while hubbing is efficient, airlines may choose a linear network for strategic reasons. Furthermore, we show that this structure softens competition by preventing contagion of competition across markets.Airlines, Competition, Capacity constraints, Network, Uncertainty

Argument Mining with Structured SVMs and RNNs

We propose a novel factor graph model for argument mining, designed for settings in which the argumentative relations in a document do not necessarily form a tree structure. (This is the case in over 20% of the web comments dataset we release.) Our model jointly learns elementary unit type classification and argumentative relation prediction. Moreover, our model supports SVM and RNN parametrizations, can enforce structure constraints (e.g., transitivity), and can express dependencies between adjacent relations and propositions. Our approaches outperform unstructured baselines in both web comments and argumentative essay datasets.Comment: Accepted for publication at ACL 2017. 11 pages, 5 figures. Code at https://github.com/vene/marseille and data at http://joonsuk.org

Encoding folding paths of RNA switches

RNA co-transcriptional folding has long been suspected to play an active role in helping proper native folding of ribozymes and structured regulatory motifs in mRNA untranslated regions. Yet, the underlying mechanisms and coding requirements for efficient co-transcriptional folding remain unclear. Traditional approaches have intrinsic limitations to dissect RNA folding paths, as they rely on sequence mutations or circular permutations that typically perturb both RNA folding paths and equilibrium structures. Here, we show that exploiting sequence symmetries instead of mutations can circumvent this problem by essentially decoupling folding paths from equilibrium structures of designed RNA sequences. Using bistable RNA switches with symmetrical helices conserved under sequence reversal, we demonstrate experimentally that native and transiently formed helices can guide efficient co-transcriptional folding into either long-lived structure of these RNA switches. Their folding path is controlled by the order of helix nucleations and subsequent exchanges during transcription, and may also be redirected by transient antisense interactions. Hence, transient intra- and intermolecular base pair interactions can effectively regulate the folding of nascent RNA molecules into different native structures, provided limited coding requirements, as discussed from an information theory perspective. This constitutive coupling between RNA synthesis and RNA folding regulation may have enabled the early emergence of autonomous RNA-based regulation networks.Comment: 9 pages, 6 figure

Genome-driven evolutionary game theory helps understand the rise of metabolic interdependencies in microbial communities

Metabolite exchanges in microbial communities give rise to ecological interactions that govern ecosystem diversity and stability. It is unclear, however, how the rise of these interactions varies across metabolites and organisms. Here we address this question by integrating genome-scale models of metabolism with evolutionary game theory. Specifically, we use microbial fitness values estimated by metabolic models to infer evolutionarily stable interactions in multi-species microbial “games”. We first validate our approach using a well-characterized yeast cheater-cooperator system. We next perform over 80,000 in silico experiments to infer how metabolic interdependencies mediated by amino acid leakage in Escherichia coli vary across 189 amino acid pairs. While most pairs display shared patterns of inter-species interactions, multiple deviations are caused by pleiotropy and epistasis in metabolism. Furthermore, simulated invasion experiments reveal possible paths to obligate cross-feeding. Our study provides genomically driven insight into the rise of ecological interactions, with implications for microbiome research and synthetic ecology.We gratefully acknowledge funding from the Defense Advanced Research Projects Agency (Purchase Request No. HR0011515303, Contract No. HR0011-15-C-0091), the U.S. Department of Energy (Grants DE-SC0004962 and DE-SC0012627), the NIH (Grants 5R01DE024468 and R01GM121950), the national Science Foundation (Grants 1457695 and NSFOCE-BSF 1635070), MURI Grant W911NF-12-1-0390, the Human Frontiers Science Program (grant RGP0020/2016), and the Boston University Interdisciplinary Biomedical Research Office ARC grant on Systems Biology Approaches to Microbiome Research. We also thank Dr Kirill Korolev and members of the Segre Lab for their invaluable feedback on this work. (HR0011515303 - Defense Advanced Research Projects Agency; HR0011-15-C-0091 - Defense Advanced Research Projects Agency; DE-SC0004962 - U.S. Department of Energy; DE-SC0012627 - U.S. Department of Energy; 5R01DE024468 - NIH; R01GM121950 - NIH; 1457695 - national Science Foundation; NSFOCE-BSF 1635070 - national Science Foundation; W911NF-12-1-0390 - MURI; RGP0020/2016 - Human Frontiers Science Program; Boston University Interdisciplinary Biomedical Research Office ARC)Published versio

Self-interaction errors in nuclear energy density functionals

When applied to a single nucleon, nuclear energy density functionals may yield a non-vanishing internal energy thus implying that the nucleon is interacting with itself. It is shown how to avoid this unphysical feature for semi-local phenomenological functionals containing all possible bilinear combinations of local densities and currents up to second order in the derivatives. The method outlined in this Rapid Communication could be easily extended to functionals containing higher order terms, and could serve as a guide for constraining the time-odd part of the functional

What is equality of opportunity in education?

There is widespread disagreement about what equality of opportunity in education requires. For some it is that each child is legally permitted to go to school. For others it is that each child receives the same educational resources. Further interpretations abound. This fact presents a problem: when politicians or academics claim they are in favour of equality of opportunity in education, it is unclear what they mean and debate is hindered by mutual misunderstanding. In this article, I introduce a framework to ameliorate this problem. More specifically, I develop an important but neglected framework for the concept of equality of opportunity and apply it to examine particular conceptions of equality of opportunity in education. In doing this, I hope to produce a piece of applied conceptual analysis that can both help clarify existing positions within the equality of opportunity in education debate and allow those seeking to produce new positions to express them more clearly

The Essential Role of String-Derived Symmetries in Ensuring Proton-Stability and Light Neutrino Masses

The paper addresses the problem of suppressing naturally the unsafe d=4 as well as the color-triplet mediated and/or gravity-linked d=5 proton-decay operators, which generically arise in SUSY-unification. It also attempts to give light masses to the neutrinos, of the type suggested by current experiments. It is noted that neither the symmetries in $SO(10)$, nor those in $E_6$, suffice for the purpose -- especially in the matter of suppressing naturally the d=5 proton-decay operators. By contrast, it is shown that a certain {\it string-derived symmetry}, which cannot arise within conventional grand unification, but which does arise within a class of three-generation string-solutions, suffices, in conjuction with $B-L$, to safeguard proton-stability from all potential dangers, including those which may arise through higher dimensional operators and the color-triplets in the infinite tower of states. At the same time, the symmetry in question permits neutrinos to acquire appropriate masses. This shows that {\it string theory plays an essential role in ensuring natural consistency of SUSY-unification with two low-energy observations -- proton-stability and light masses for the neutrinos}. The correlation between the masses of the extra $Z'$-boson (or bosons), which arise in these models, and proton-decay rate is noted.Comment: 20 pages, plain LaTeX. Footnote 26 expanded to include implication of neutrino-higgsino mixing, and two new footnotes adde