3,723 research outputs found

    Putting the Pieces Together for Good Governance of REDD+: An Analysis of 32 REDD+ Country Readiness Proposals

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    Developing countries are receiving new financial and technical support to design and implement programs that reduce emissions from deforestation and forest degradation (referred to as REDD+). Reducing emissions from forest cover change requires transparent, accountable, inclusive, and coordinated systems and institutions to govern REDD+ programs. Two multilateral initiatives -- the World Bank-administered Forest Carbon Partnership Facility (FCPF) and the United Nations Collaborative Programme on Reducing Emissions from Deforestation and Forest Degradation in developing countries (UN-REDD Programme) -- are supporting REDD+ countries to become "ready" for REDD+ by preparing initial strategy proposals, developing institutions to manage REDD+ programs, and building capacity to implement REDD+ activities. This paper reviews 32 REDD+ readiness proposals submitted to these initiatives to understand overall trends in how eight elements of readiness (referred to in this paper as readiness needs) are being understood and prioritized globally. Specifically, we assess whether the readiness proposals (i) identify the eight readiness needs as relevant for REDD+, (ii) discuss challenges and options for addressing each need, and (iii) identify next steps to be implemented in relation to each need. Our analysis found that the readiness proposals make important commitments to developing effective, equitable, and well-governed REDD+ programs. However, in many of the proposals these general statements have not yet been translated into clear next steps

    Enumeration of totally positive Grassmann cells

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    Alex Postnikov has given a combinatorially explicit cell decomposition of the totally nonnegative part of a Grassmannian, denoted Gr_{kn}+, and showed that this set of cells is isomorphic as a graded poset to many other interesting graded posets. The main result of this paper is an explicit generating function which enumerates the cells in Gr_{kn}+ according to their dimension. As a corollary, we give a new proof that the Euler characteristic of Gr_{kn}+ is 1. Additionally, we use our result to produce a new q-analog of the Eulerian numbers, which interpolates between the Eulerian numbers, the Narayana numbers, and the binomial coefficients.Comment: 21 pages, 10 figures. Final version, with references added and minor corrections made, to appear in Advances in Mathematic

    Girls' Economic Security in the Washington Region

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    This issue brief highlights key issues and demographic trends in the Washington region, and dives specifically into issues of poverty and opportunity that affect girls' capacity to attain economic security in adulthood. Our objective is to better understand girls' experiences and circumstances and to work together with the community to identify strategies that reduce barriers, increase opportunities and increase the number of girls who are able to live economically secure lives both today and for generations to come

    Tableaux combinatorics for the asymmetric exclusion process and Askey-Wilson polynomials

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    Introduced in the late 1960's, the asymmetric exclusion process (ASEP) is an important model from statistical mechanics which describes a system of interacting particles hopping left and right on a one-dimensional lattice of n sites with open boundaries. It has been cited as a model for traffic flow and protein synthesis. In the most general form of the ASEP with open boundaries, particles may enter and exit at the left with probabilities alpha and gamma, and they may exit and enter at the right with probabilities beta and delta. In the bulk, the probability of hopping left is q times the probability of hopping right. The first main result of this paper is a combinatorial formula for the stationary distribution of the ASEP with all parameters general, in terms of a new class of tableaux which we call staircase tableaux. This generalizes our previous work for the ASEP with parameters gamma=delta=0. Using our first result and also results of Uchiyama-Sasamoto-Wadati, we derive our second main result: a combinatorial formula for the moments of Askey-Wilson polynomials. Since the early 1980's there has been a great deal of work giving combinatorial formulas for moments of various other classical orthogonal polynomials (e.g. Hermite, Charlier, Laguerre, Meixner). However, this is the first such formula for the Askey-Wilson polynomials, which are at the top of the hierarchy of classical orthogonal polynomials.Comment: An announcement of these results appeared here: http://www.pnas.org/content/early/2010/03/25/0909915107.abstract This version of the paper has updated references and corrects a gap in the proof of Proposition 6.11 which was in the published versio

    Total positivity for cominuscule Grassmannians

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    In this paper we explore the combinatorics of the non-negative part (G/P)+ of a cominuscule Grassmannian. For each such Grassmannian we define Le-diagrams -- certain fillings of generalized Young diagrams which are in bijection with the cells of (G/P)+. In the classical cases, we describe Le-diagrams explicitly in terms of pattern avoidance. We also define a game on diagrams, by which one can reduce an arbitrary diagram to a Le-diagram. We give enumerative results and relate our Le-diagrams to other combinatorial objects. Surprisingly, the totally non-negative cells in the open Schubert cell of the odd and even orthogonal Grassmannians are (essentially) in bijection with preference functions and atomic preference functions respectively.Comment: 39 page

    Discrete Morse theory for totally non-negative flag varieties

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    In a seminal 1994 paper, Lusztig extended the theory of total positivity by introducing the totally non-negative part (G/P)_{\geq 0} of an arbitrary (generalized, partial) flag variety G/P. He referred to this space as a "remarkable polyhedral subspace", and conjectured a decomposition into cells, which was subsequently proven by the first author. Subsequently the second author made the concrete conjecture that this cell decomposed space is the next best thing to a polyhedron, by conjecturing it to be a regular CW complex that is homeomorphic to a closed ball. In this article we use discrete Morse theory to prove this conjecture up to homotopy-equivalence. Explicitly, we prove that the boundaries of the cells are homotopic to spheres, and the closures of cells are contractible. The latter part generalizes a result of Lusztig's that (G/P)_{\geq 0} -- the closure of the top-dimensional cell -- is contractible. Concerning our result on the boundaries of cells, even the special case that the boundary of the top-dimensional cell (G/P)_{> 0} is homotopic to a sphere, is new for all G/P other than projective space.Comment: 30 page