661 research outputs found
Loading system mechanism for dielectric elastomer generators with equi-biaxial state of deformation
Dielectric Elastomer Generators (DEGs) are devices that employ a cyclically variable membrane capacitor to produce electricity from oscillating sources of mechanical energy. Capacitance variation is obtained thanks to the use of dielectric and conductive layers that can undergo different states of deformation including: uniform or non-uniform and uni- or multi-axial stretching. Among them, uniform equi-biaxial stretching is reputed as being the most effective state of deformation that maximizes the amount of energy that can be extracted in a cycle by a unit volume of Dielectric Elastomer (DE) material. This paper presents a DEG concept, with linear input motion and tunable impedance, that is based on a mechanical loading system for inducing uniform equi-biaxial states of deformation. The presented system employs two circular DE membrane capacitors that are arranged in an agonist-antagonist configuration. An analytical model of the overall system is developed and used to find the optimal design parameters that make it possible to tune the elastic response of the generator over the range of motion of interest. An apparatus is developed for the equi-biaxial testing of DE membranes and used for the experimental verification of the employed numerical models
Active Keyword Selection to Track Evolving Topics on Twitter
How can we study social interactions on evolving topics at a mass scale? Over
the past decade, researchers from diverse fields such as economics, political
science, and public health have often done this by querying Twitter's public
API endpoints with hand-picked topical keywords to search or stream
discussions. However, despite the API's accessibility, it remains difficult to
select and update keywords to collect high-quality data relevant to topics of
interest. In this paper, we propose an active learning method for rapidly
refining query keywords to increase both the yielded topic relevance and
dataset size. We leverage a large open-source COVID-19 Twitter dataset to
illustrate the applicability of our method in tracking Tweets around the key
sub-topics of Vaccine, Mask, and Lockdown. Our experiments show that our method
achieves an average topic-related keyword recall 2x higher than baselines. We
open-source our code along with a web interface for keyword selection to make
data collection from Twitter more systematic for researchers.Comment: 10 pages, 3 figure
Recommended from our members
A Note on the Unconditional Bias of the Nadaraya-Watson Regression Estimator
In this note we investigate the order of the unconditional bias of the Nadarya-Watson (Nadaraya, 1964; Watson, 1964) estimator for a multivariate regression. Surprisingly, previous attempts in establishing this result are either imprecise and technically deficient, or of limited use given the assumptions imposed (see inter alia, Glad (1998), Mack and MĂĽller (1988), Pagan and Ullah (1999), and Scott (2015)). The results are also often conflicting (see inter alia, Choi et al. (2000), Chu and Marron (1991), Collomb (1981), and Glad (1998)). Unfortunately, our result here is incomplete, but we highlight the issues and suggest further ideas to resolve them
Stochastic Water Balance Dynamics of Passive and Controlled Stormwater Basins
Urbanization and changing rainfall intensities affect the performance of urban stormwater infrastructure, creating the necessity to design resilient stormwater systems. One proposed method to increase the resilience of stormwater infrastructure is the active control of system flows. To improve the understanding of actively-controlled urban water infrastructure function under variable hydro-climate, we develop a stochastic water balance model for stormwater retention and detention basins with both passive and actively-controlled outflow structures. Under active outflow control, the outflow valve is closed until the water level in the basin reaches a specified maximum at which point the valve opens and the basin empties. Using the stochastic water balance model, we develop analytical expressions for the steady-state probability density functions (PDFs) of water level and valve closure time, as well as the joint PDF of water level and valve closure time. These PDFs then are used to define water level and flow duration curves that provide a probabilistic description of the full range of basin performance. The model accurately predicts the water level PDF estimated from data collected at a retention basin with a passive outflow structure. The model provides a basis for evaluating how changes in the rainfall-runoff process, affected by land use and climate change, will impact the variability of stormwater basin water storage and pollutant removal function. We find that this variability can be managed through the adaptive updating of the active control rule for the outflow structure
Towards Reliable Misinformation Mitigation: Generalization, Uncertainty, and GPT-4
Misinformation poses a critical societal challenge, and current approaches
have yet to produce an effective solution. We propose focusing on
generalization, soft classification, and leveraging recent large language
models to create more practical tools in contexts where perfect predictions
remain unattainable. We begin by demonstrating that GPT-4 and other language
models can outperform existing methods in the literature. Next, we explore
their generalization, revealing that GPT-4 and RoBERTa-large exhibit critical
differences in failure modes, which offer potential for significant performance
improvements. Finally, we show that these models can be employed in soft
classification frameworks to better quantify uncertainty. We find that models
with inferior hard classification results can achieve superior soft
classification performance. Overall, this research lays groundwork for future
tools that can drive real-world progress on misinformation
Open, Closed, or Small Language Models for Text Classification?
Recent advancements in large language models have demonstrated remarkable
capabilities across various NLP tasks. But many questions remain, including
whether open-source models match closed ones, why these models excel or
struggle with certain tasks, and what types of practical procedures can improve
performance. We address these questions in the context of classification by
evaluating three classes of models using eight datasets across three distinct
tasks: named entity recognition, political party prediction, and misinformation
detection. While larger LLMs often lead to improved performance, open-source
models can rival their closed-source counterparts by fine-tuning. Moreover,
supervised smaller models, like RoBERTa, can achieve similar or even greater
performance in many datasets compared to generative LLMs. On the other hand,
closed models maintain an advantage in hard tasks that demand the most
generalizability. This study underscores the importance of model selection
based on task requirementsComment: 14 pages, 15 Tables, 1 Figur
The Rayleigh-Lamb wave propagation in dielectric elastomer layers subjected to large deformations
The propagation of waves in soft dielectric elastomer layers is investigated.
To this end incremental motions superimposed on homogeneous finite deformations
induced by bias electric fields and pre-stretch are determined. First we
examine the case of mechanically traction-free layer, which is an extension of
the Rayleigh-Lamb problem in the purely elastic case. Two other loading
configurations are accounted for too. Subsequently, numerical examples for the
dispersion relations are evaluated for a dielectric solid governed by an
augmented neo-Hookean strain energy. It is found that the the phase speeds and
frequencies strongly depend on the electric excitation and pre-stretch. These
findings lend themselves at the possibility of controlling the propagation
velocity as well as filtering particular frequencies with suitable choices of
the electric bias field
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