1,808 research outputs found
"Objective" Ambiguity and Ex Ante Trade
We explore the implications of assuming that individuals have maxmin preferences incorporating objective but imprecise probabilistic information on the features of Pareto optimal allocations
A Methodology for the Optimization of Disaggregated Space System Conceptual Designs
Optimal design techniques have proven to be an effective systems engineering tool. Using systems architecture as the foundation, this research explores the use of mixed variable optimization models for synthesizing and evaluating disaggregated space system concepts. Model-based conceptual design techniques are used to identify and assess system architectures based upon estimated system cost, performance trades, and cost risk. The Disaggregated Integral System Concept Optimization (DISCO) methodology is introduced, and then applied to representative space-based missions. Several results are obtained that indicate significant cost effectiveness gains from the optimization of multi-orbit and multi-function/multi-orbit disaggregated space systems. The general methodology has broad applicability for model-based conceptual design (MBCD) of many system types, but is particularly useful for dynamic disaggregated space systems
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Configurations and colouring problems in block designs
A Steiner triple system of order v (STS(v)) is called x-chromatic if x is the smallest number of colours needed to avoid monochromatic blocks. Amongst our results on colour class structures we show that every STS (19) is 3- or 4-chromatic, that every 3-chromatic STS(19) has an equitable 3-colouring (meaning that the colours are as uniformly distributed as possible), and that for all admissible v > 25 there exists a 3-chromatic STS(v) which does not admit an equitable 3-colouring. We obtain a formula for the number of independent sets in an STS(v) and use it to show that an STS(21) must contain eight independent points. This leads to a simple proof that every STS(21) is 3- or 4-chromatic. Substantially extending existing tabulations, we provide an enumeration of STS trades of up to 12 blocks, and as an application we show that any pair of STS(15)s must be 3-1-isomorphic. We prove a general theorem that enables us to obtain formulae for the frequencies of occurrence of configurations in triple systems. Some of these are used in our proof that for v > 25 no STS(u) has a 3-existentially closed block intersection graph. Of specific interest in connection with a conjecture of Erdos are 6-sparse and perfect Steiner triple systems, characterized by the avoidance of specific configurations. We describe two direct constructions that produce 6-sparse STS(v)s and we give a recursive construction that preserves 6-sparseness. Also we settle an old question concerning the occurrence of perfect block transitive Steiner triple systems. Finally, we consider Steiner 5(2,4, v) designs that are built from collections of Steiner triple systems. We solve a longstanding problem by constructing such systems with v = 61 (Zoe’s design) and v = 100 (the design of the century)
Topological Anomaly Detection in Dynamic Multilayer Blockchain Networks
Motivated by the recent surge of criminal activities with
cross-cryptocurrency trades, we introduce a new topological perspective to
structural anomaly detection in dynamic multilayer networks. We postulate that
anomalies in the underlying blockchain transaction graph that are composed of
multiple layers are likely to also be manifested in anomalous patterns of the
network shape properties. As such, we invoke the machinery of clique persistent
homology on graphs to systematically and efficiently track evolution of the
network shape and, as a result, to detect changes in the underlying network
topology and geometry. We develop a new persistence summary for multilayer
networks, called stacked persistence diagram, and prove its stability under
input data perturbations. We validate our new topological anomaly detection
framework in application to dynamic multilayer networks from the Ethereum
Blockchain and the Ripple Credit Network, and demonstrate that our stacked PD
approach substantially outperforms state-of-art techniques.Comment: 26 pages, 6 figures, 7 table
Defining, Valuing, and Providing Ecosystem Goods and Services
Ecosystem services are the specific results of ecosystem processes that either directly sustain or enhance human life (as does natural protection from the sun's harmful ultraviolet rays) or maintain the quality of ecosystem goods (as water purification maintains the quality of streamflow). "Ecosystem service" has come to represent several related topics ranging from the measurement to the marketing of ecosystem service flows. In this article we examine several of these topics by first clarifying the meaning of "ecosystem service" and then (1) placing ecosystem goods and services within an economic framework, emphasizing the role and limitations of substitutes; (2) summarizing the methods for valuation of ecosystem goods and services; and (3) reviewing the various approaches for their provision and financing.Many ecosystem services and some ecosystem goods are received without monetary payment. The "marketing" of ecosystem goods and services is basically an effort to turn such recipients - those who benefit without ownership- into buyers, thereby providing market signals that serve to help protect valuable goods and services. We review various formal arrangements for making this happen
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