2,040 research outputs found
Order of magnitude time-reversible Markov chains and characterization of clustering processes
We introduce the notion of order of magnitude reversibility
(OM-reversibility) in Markov chains that are parametrized by a positive
parameter \ep. OM-reversibility is a weaker condition than reversibility, and
requires only the knowledge of order of magnitude of the transition
probabilities. For an irreducible, OM-reversible Markov chain on a finite state
space, we prove that the stationary distribution satisfies order of magnitude
detailed balance (analog of detailed balance in reversible Markov chains). The
result characterizes the states with positive probability in the limit of the
stationary distribution as \ep \to 0, which finds an important application in
the case of singularly perturbed Markov chains that are reducible for \ep=0.
We show that OM-reversibility occurs naturally in macroscopic systems,
involving many interacting particles. Clustering is a common phenomenon in
biological systems, in which particles or molecules aggregate at one location.
We give a simple condition on the transition probabilities in an interacting
particle Markov chain that characterizes clustering. We show that such
clustering processes are OM-reversible, and we find explicitly the order of
magnitude of the stationary distribution. Further, we show that the single pole
states, in which all particles are at a single vertex, are the only states with
positive probability in the limit of the stationary distribution as the rate of
diffusion goes to zero.Comment: 22 pages, 3 figure
A survey of methods for deciding whether a reaction network is multistationary
Which reaction networks, when taken with mass-action kinetics, have the
capacity for multiple steady states? There is no complete answer to this
question, but over the last 40 years various criteria have been developed that
can answer this question in certain cases. This work surveys these
developments, with an emphasis on recent results that connect the capacity for
multistationarity of one network to that of another. In this latter setting, we
consider a network that is embedded in a larger network , which means
that is obtained from by removing some subsets of chemical species and
reactions. This embedding relation is a significant generalization of the
subnetwork relation. For arbitrary networks, it is not true that if is
embedded in , then the steady states of lift to . Nonetheless, this
does hold for certain classes of networks; one such class is that of fully open
networks. This motivates the search for embedding-minimal multistationary
networks: those networks which admit multiple steady states but no proper,
embedded networks admit multiple steady states. We present results about such
minimal networks, including several new constructions of infinite families of
these networks
An SSE approach to reusability
The SSE project has engineering analysis and design efforts under way for the development of the SSE reusability library management system. An ad hoc committee on reuse has been meeting for several months identifying design considerations and learning about Ruben Prieto-Diaz faceted classification, CAMP domain analysis, SPC activities, SEI activities, and SPS activities. A standard format was developed for the Ada prologue for reusable components (both specification and body). The SSE reusability process can be viewed as a transformation process with minimized losses and difficulties
Open Vocabulary Learning on Source Code with a Graph-Structured Cache
Machine learning models that take computer program source code as input
typically use Natural Language Processing (NLP) techniques. However, a major
challenge is that code is written using an open, rapidly changing vocabulary
due to, e.g., the coinage of new variable and method names. Reasoning over such
a vocabulary is not something for which most NLP methods are designed. We
introduce a Graph-Structured Cache to address this problem; this cache contains
a node for each new word the model encounters with edges connecting each word
to its occurrences in the code. We find that combining this graph-structured
cache strategy with recent Graph-Neural-Network-based models for supervised
learning on code improves the models' performance on a code completion task and
a variable naming task --- with over relative improvement on the latter
--- at the cost of a moderate increase in computation time.Comment: Published in the International Conference on Machine Learning (ICML
2019), 13 page
Dimensions and Determinants of Peoples’ Participation in Watershed Development Programmes in Rajasthan
Peoples’ participation has been at the centre-stage of the resource conservation and rural development efforts in the developing countries. The study on peoples’ participation in watershed development programmes in Rajasthan has revealed that a very low proportion of beneficiaries is contributing at different stages of the programme in terms of either labour or finances or both. The determinants of participation have been identified using Tobit regression. The institutional effectiveness has been found as the key factor towards guaranteeing involvement of people in the watershed programmes. The other factors positively related with peoples’ participation are training of farmers, age, and frequency of the visit of extension workers. A negative relationship has been found between participation and off-farm income. Therefore, efforts should be made for developing effective local institutions, capacity building through training of farmers and providing off-farm employment opportunities in the countryside itself for safeguarding the livelihoods of people in the rainfed areas.Agricultural and Food Policy,
La Fusta. Patrimoni cultural i biològic
Wood: biological and cultural heritage. Anthracology is a branch of archaeobotany that came into being at the beginning of the 20th Century for the botanical identification of prehistoric wood and carbon. The goals are paleoecological, ethnological and methodological. The protocol followed for this analysis involves the observation of plant tissues under reflected-light microscopy and scanning electron microscopy to identify the material botanically. In recent years, this kind of analysis is being applied to heritage objects and those in restoration; here we will give some examples: an historic object, the restoration of a monument and the reconstruction of a prehistoric landscape
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