Low speed wind tunnel investigation of a four-engine upper surface blown model having swept wing and rectangular and D-shaped exhaust nozzles

A low speed investigation was conducted in the Langley V/STOL tunnel to determine the power-on static-turning and powered-lift aerodynamic performance of a four engine upper surface blown transport configuration. Initial tests with a D-shaped exhaust nozzle showed relatively poor flow-turning capability, and the D-nozzles were replaced by rectangular nozzles with a width-height ratio of 6.0. The high lift system consisted of a leading edge slat and two different trailing-edge-flap configurations. A double slotted flap with the gaps sealed was investigated and a simple radius flap was also tested. A maximum lift coefficient of approximately 9.3 was obtained for the model with the rectangular exhaust nozzles with both the double slotted flap deflected 50 deg and the radius flap deflected 90 deg

Wing surface-jet interaction characteristics of an upper-surface blown model with rectangular exhaust nozzles and a radius flap

The wing surface jet interaction characteristics of an upper surface blown transport configuration were investigated in the Langley V/STOL tunnel. Velocity profiles at the inboard engine center line were measured for several chordwise locations, and chordwise pressure distributions on the flap were obtained. The model represented a four engine arrangement having relatively high aspect ratio rectangular spread, exhaust nozzles and a simple trailing edge radius flap

Near-Optimal Computation of Runs over General Alphabet via Non-Crossing LCE Queries

Longest common extension queries (LCE queries) and runs are ubiquitous in algorithmic stringology. Linear-time algorithms computing runs and preprocessing for constant-time LCE queries have been known for over a decade. However, these algorithms assume a linearly-sortable integer alphabet. A recent breakthrough paper by Bannai et.\ al.\ (SODA 2015) showed a link between the two notions: all the runs in a string can be computed via a linear number of LCE queries. The first to consider these problems over a general ordered alphabet was Kosolobov (\emph{Inf.\ Process.\ Lett.}, 2016), who presented an $O(n (\log n)^{2/3})$-time algorithm for answering $O(n)$ LCE queries. This result was improved by Gawrychowski et.\ al.\ (accepted to CPM 2016) to $O(n \log \log n)$ time. In this work we note a special \emph{non-crossing} property of LCE queries asked in the runs computation. We show that any $n$ such non-crossing queries can be answered on-line in $O(n \alpha(n))$ time, which yields an $O(n \alpha(n))$-time algorithm for computing runs

Polyhedral models for generalized associahedra via Coxeter elements

Motivated by the theory of cluster algebras, F. Chapoton, S. Fomin and A. Zelevinsky associated to each finite type root system a simple convex polytope called \emph{generalized associahedron}. They provided an explicit realization of this polytope associated with a bipartite orientation of the corresponding Dynkin diagram. In the first part of this paper, using the parametrization of cluster variables by their $g$-vectors explicitly computed by S.-W. Yang and A. Zelevinsky, we generalize the original construction to any orientation. In the second part we show that our construction agrees with the one given by C. Hohlweg, C. Lange, and H. Thomas in the setup of Cambrian fans developed by N. Reading and D. Speyer.Comment: 31 pages, 2 figures. Changelog: 20111106: initial version 20120403: fixed errors in figures 20120827: revised versio

Associahedra via spines

An associahedron is a polytope whose vertices correspond to triangulations of a convex polygon and whose edges correspond to flips between them. Using labeled polygons, C. Hohlweg and C. Lange constructed various realizations of the associahedron with relevant properties related to the symmetric group and the classical permutahedron. We introduce the spine of a triangulation as its dual tree together with a labeling and an orientation. This notion extends the classical understanding of the associahedron via binary trees, introduces a new perspective on C. Hohlweg and C. Lange's construction closer to J.-L. Loday's original approach, and sheds light upon the combinatorial and geometric properties of the resulting realizations of the associahedron. It also leads to noteworthy proofs which shorten and simplify previous approaches.Comment: 27 pages, 11 figures. Version 5: minor correction

Multi-triangulations as complexes of star polygons

Maximal $(k+1)$-crossing-free graphs on a planar point set in convex position, that is, $k$-triangulations, have received attention in recent literature, with motivation coming from several interpretations of them. We introduce a new way of looking at $k$-triangulations, namely as complexes of star polygons. With this tool we give new, direct, proofs of the fundamental properties of $k$-triangulations, as well as some new results. This interpretation also opens-up new avenues of research, that we briefly explore in the last section.Comment: 40 pages, 24 figures; added references, update Section

Many non-equivalent realizations of the associahedron

Hohlweg and Lange (2007) and Santos (2004, unpublished) have found two different ways of constructing exponential families of realizations of the n-dimensional associahedron with normal vectors in {0,1,-1}^n, generalizing the constructions of Loday (2004) and Chapoton-Fomin-Zelevinsky (2002). We classify the associahedra obtained by these constructions modulo linear equivalence of their normal fans and show, in particular, that the only realization that can be obtained with both methods is the Chapoton-Fomin-Zelevinsky (2002) associahedron. For the Hohlweg-Lange associahedra our classification is a priori coarser than the classification up to isometry of normal fans, by Bergeron-Hohlweg-Lange-Thomas (2009). However, both yield the same classes. As a consequence, we get that two Hohlweg-Lange associahedra have linearly equivalent normal fans if and only if they are isometric. The Santos construction, which produces an even larger family of associahedra, appears here in print for the first time. Apart of describing it in detail we relate it with the c-cluster complexes and the denominator fans in cluster algebras of type A. A third classical construction of the associahedron, as the secondary polytope of a convex n-gon (Gelfand-Kapranov-Zelevinsky, 1990), is shown to never produce a normal fan linearly equivalent to any of the other two constructions.Comment: 30 pages, 13 figure

Chronic Viral Infection and Primary Central Nervous System Malignancy

Primary central nervous system (CNS) tumors cause significant morbidity and mortality in both adults and children. While some of the genetic and molecular mechanisms of neuro-oncogenesis are known, much less is known about possible epigenetic contributions to disease pathophysiology. Over the last several decades, chronic viral infections have been associated with a number of human malignancies. In primary CNS malignancies, two families of viruses, namely polyomavirus and herpesvirus, have been detected with varied frequencies in a number of pediatric and adult histological tumor subtypes. However, establishing a link between chronic viral infection and primary CNS malignancy has been an area of considerable controversy, due in part to variations in detection frequencies and methodologies used among researchers. Since a latent viral neurotropism can be seen with a variety of viruses and a widespread seropositivity exists among the population, it has been difficult to establish an association between viral infection and CNS malignancy based on epidemiology alone. While direct evidence of a role of viruses in neuro-oncogenesis in humans is lacking, a more plausible hypothesis of neuro-oncomodulation has been proposed. The overall goals of this review are to summarize the many human investigations that have studied viral infection in primary CNS tumors, discuss potential neuro-oncomodulatory mechanisms of viral-associated CNS disease and propose future research directions to establish a more firm association between chronic viral infections and primary CNS malignancies