2,095 research outputs found
Dirichlet belief networks for topic structure learning
Recently, considerable research effort has been devoted to developing deep
architectures for topic models to learn topic structures. Although several deep
models have been proposed to learn better topic proportions of documents, how
to leverage the benefits of deep structures for learning word distributions of
topics has not yet been rigorously studied. Here we propose a new multi-layer
generative process on word distributions of topics, where each layer consists
of a set of topics and each topic is drawn from a mixture of the topics of the
layer above. As the topics in all layers can be directly interpreted by words,
the proposed model is able to discover interpretable topic hierarchies. As a
self-contained module, our model can be flexibly adapted to different kinds of
topic models to improve their modelling accuracy and interpretability.
Extensive experiments on text corpora demonstrate the advantages of the
proposed model.Comment: accepted in NIPS 201
Active network management for electrical distribution systems: problem formulation, benchmark, and approximate solution
With the increasing share of renewable and distributed generation in
electrical distribution systems, Active Network Management (ANM) becomes a
valuable option for a distribution system operator to operate his system in a
secure and cost-effective way without relying solely on network reinforcement.
ANM strategies are short-term policies that control the power injected by
generators and/or taken off by loads in order to avoid congestion or voltage
issues. Advanced ANM strategies imply that the system operator has to solve
large-scale optimal sequential decision-making problems under uncertainty. For
example, decisions taken at a given moment constrain the future decisions that
can be taken and uncertainty must be explicitly accounted for because neither
demand nor generation can be accurately forecasted. We first formulate the ANM
problem, which in addition to be sequential and uncertain, has a nonlinear
nature stemming from the power flow equations and a discrete nature arising
from the activation of power modulation signals. This ANM problem is then cast
as a stochastic mixed-integer nonlinear program, as well as second-order cone
and linear counterparts, for which we provide quantitative results using state
of the art solvers and perform a sensitivity analysis over the size of the
system, the amount of available flexibility, and the number of scenarios
considered in the deterministic equivalent of the stochastic program. To foster
further research on this problem, we make available at
http://www.montefiore.ulg.ac.be/~anm/ three test beds based on distribution
networks of 5, 33, and 77 buses. These test beds contain a simulator of the
distribution system, with stochastic models for the generation and consumption
devices, and callbacks to implement and test various ANM strategies
Transnational Municipal Networks: Local action on climate change through global networks
Transnational Municipal Networks (TMNs) are prominent networks in the international climate governance arena serving as drivers of and advocates for local action on climate change. The main objective of this exploratory research is to establish the relation between the internal governance structure of the TMNs and their ability to carry out certain types of activities. Internal governance encompasses the means through which a TMN regulates the authority and structure within the organization. External governance refers to interaction of the network with other stakeholders and the ability to respond to external pressures as well as to position the operation of the network in the multi-level climate governance arena. From the examined cases, namely ICLEI Local Governments for Sustainability (ICLEI), C40 Cities Climate Leadership Group (C40), and 100 Resilient Cities (100RC), and a networking event, it is clear that there is a considerable amount of similar internal governance practices utilised by networks with different historical backgrounds and structures. The applied analytical criteria, based on a framework developed by Kern and Bulkeley (2009), constituted such arrangements as information and communication, project funding and cooperation, and recognition, benchmarking and certification. These can be seen to be instrumental in delineating internal governance formation of the network. Considering key functional aspirations of TMNs which include learning, advocacy and financing, the examination of their internal governance architecture lead to the suggestion that there are preferred methods of internal governing capable of synergistic relation with the external governance dimensions and, hence, facilitating performance of their functions. Established patterns were evaluated in the context of international climate governance to reveal the importance of collaborative and cooperative interactions, climate negotiations and climate financing mechanisms in determining the factors potentially affecting the internal governance composition of TMNs
Institutionalising city networking: Discursive and rational choice institutional perspectives on membership of transnational municipal networks
This article analyses participants’ reasoning for their city’s membership in transnational municipal networks and the extent to which this changes over time. Theoretically, we build on new-institutional theory and conclude that although parts of the members’ reasoning have rational components, a discursive institutional perspective improves the understanding of cities’ membership of transnational municipal networks. This perspective uncovers how important aspects of transnational municipal network participation are motivated by a different logic than that of measurable output. Cities use transnational municipal networks as sources of internal and external legitimacy, to legitimatise their position in domestic politics and their international position among other ‘global’ cities.publishedVersio
Evaluation of GaN-HEMT power amplifiers using BST-based components for load modulation
Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.In this paper, the concept of load-modulated power amplifiers (PAs) is studied. Two GaN-HEMT power amplifiers (PAs), targeted for high efficiency at maximum and output back-off (OBO) power levels, are designed, implemented, and tested across 1.8–2.2 GHz. The load modulation in the first design is realized by tuning the shunt capacitors in the output matching network. A novel method is employed in the second design, where barium–stronrium–titante is used for the realization of load modulation. The large-signal measurement results across the desired band show 59–70% drain efficiency at 44–44.5 dBm output power for both designs. Using the available tunable technique, the drain efficiency of the PAs is enhanced by 4–20% at 6 dB OBO across the bandwidth
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