8,835 research outputs found
Syntactic Topic Models
The syntactic topic model (STM) is a Bayesian nonparametric model of language
that discovers latent distributions of words (topics) that are both
semantically and syntactically coherent. The STM models dependency parsed
corpora where sentences are grouped into documents. It assumes that each word
is drawn from a latent topic chosen by combining document-level features and
the local syntactic context. Each document has a distribution over latent
topics, as in topic models, which provides the semantic consistency. Each
element in the dependency parse tree also has a distribution over the topics of
its children, as in latent-state syntax models, which provides the syntactic
consistency. These distributions are convolved so that the topic of each word
is likely under both its document and syntactic context. We derive a fast
posterior inference algorithm based on variational methods. We report
qualitative and quantitative studies on both synthetic data and hand-parsed
documents. We show that the STM is a more predictive model of language than
current models based only on syntax or only on topics
Methodology for designing accelerated aging tests for predicting life of photovoltaic arrays
A methodology for designing aging tests in which life prediction was paramount was developed. The methodology builds upon experience with regard to aging behavior in those material classes which are expected to be utilized as encapsulant elements, viz., glasses and polymers, and upon experience with the design of aging tests. The experiences were reviewed, and results are discussed in detail
Implementing and reasoning about hash-consed data structures in Coq
We report on four different approaches to implementing hash-consing in Coq
programs. The use cases include execution inside Coq, or execution of the
extracted OCaml code. We explore the different trade-offs between faithful use
of pristine extracted code, and code that is fine-tuned to make use of OCaml
programming constructs not available in Coq. We discuss the possible
consequences in terms of performances and guarantees. We use the running
example of binary decision diagrams and then demonstrate the generality of our
solutions by applying them to other examples of hash-consed data structures
The hardness of perfect phylogeny, feasible register assignment and other problems on thin colored graphs
AbstractIn this paper, we consider the complexity of a number of combinatorial problems; namely, Intervalizing Colored Graphs (DNA physical mapping), Triangulating Colored Graphs (perfect phylogeny), (Directed) (Modified) Colored Cutwidth, Feasible Register Assignment and Module Allocation for graphs of bounded pathwidth. Each of these problems has as a characteristic a uniform upper bound on the tree or path width of the graphs in “yes”-instances. For all of these problems with the exceptions of Feasible Register Assignment and Module Allocation, a vertex or edge coloring is given as part of the input. Our main results are that the parameterized variant of each of the considered problems is hard for the complexity classes W[t] for all t∈N. We also show that Intervalizing Colored Graphs, Triangulating Colored Graphs, and Colored Cutwidth are NP-Complete
The effect of light-limitation on spinescent structural defence and its implications on resistance to herbivory in the shade
Plants can resist herbivore pressure through structural or chemical defence or both. The ultimate
goal of defence against herbivory is to reduce the amount of damage to biomass, but more
specifically to protect against damage to meristematic tissue. The defences employed depend on the
type of herbivory experienced, which is contingent on the herbivore and its mouthparts. This
investigation was concerned with structural defence presented by spines. This type of defence
protects against mammalian herbivores such as browsers. Spiny species do not dominate in low-light
deep forest environments. Therefore the aim of this study was to determine the constraints on
spines as a defence strategy under shaded conditions by assessing the effect of reduced light on
spine efficiency. Spine efficiency was defined as the amount of defence afforded the plant given the
resources available. Spines require carbon to be built and need to be arranged properly in order to
present an adequate defence. Thus two non-mutually exclusive hypotheses were proposed: Light
limitation reduces the ability of spines to present an adequate defence against browsers due to the
architectural strategy employed and/or its influence on carbon gain. The spinescent plant chosen for
study was Carissa macrocarpa (Ecklon) A.DC. Light condition of plants was determined using
hemispherical photography. Spine efficiency of sun and shade plants was determined using a bite
test and was evaluated using architectural and physiological analyses. Architectural analysis involved
identifying levels of organisation within the plant across ontogeny and indentifying sun and shade
growth strategies. Physiological analysis involved determining carbon gain of sun and shade
individuals using gas-exchange measurements, as well as the measurement of biomass allocation by
harvesting and oven drying different plant parts. Results showed that biomass allocation patterns of
C.macrocarpa did not change in sun and shade but total biomass increased from shade to sunlit
conditions. Architectural analysis revealed that in the sun the plant adopted a stout dense structure
with high spine efficiency, while in the shade it was more elongated with lower spine efficiency.
Therefore C.macrocarpa adapts to the light environment by adopting either the shade or the sun
architectural strategy. The way in which this works is that light affects carbon gain, which either
increases or decreases biomass and in turn leads the plant to adopt the sun or shade architectural
strategy. The architectural strategy affects spine efficiency such that plants in the sun have higher
spine efficiency than plants in the shade. Thus, spinescent plants do not do well in light limited
environments because they are architecturally constrained to elongate in such conditions. This
constraint would put them at higher risk of browser damage than plants in light-sufficient
conditions, ultimately decreasing their fitness. If the patterns observed in C. macrocarpa prove to be
general, then it helps to explain why spiny plants are more commonly found in open, sunlit
environments than in deep shade
An Integrated CVaR and Real Options Approach to Investments in the Energy Sector
The objective of this paper is to combine a real options framework with portfolio optimization techniques and to apply this new framework to investments in the electricity sector. In particular, a real options model is used to assess the adoption decision of particular technologies under uncertainty. These technologies are coal-fired power plants, biomass-fired power plants and onshore wind mills, and they are representative of technologies based on fossil fuels, biomass and renewables, respectively. The return distributions resulting from this analysis are then used as an input to a portfolio optimization, where the measure of risk is the Conditional Value-at-Risk (CVaR)
Scheduling language and algorithm development study. Volume 3, phase 2: As-built specifications for the prototype language and module library
Detailed specifications of the prototype language and module library are presented. The user guide to the translator writing system is included
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