435 research outputs found
Geodesic Distance Function Learning via Heat Flow on Vector Fields
Learning a distance function or metric on a given data manifold is of great
importance in machine learning and pattern recognition. Many of the previous
works first embed the manifold to Euclidean space and then learn the distance
function. However, such a scheme might not faithfully preserve the distance
function if the original manifold is not Euclidean. Note that the distance
function on a manifold can always be well-defined. In this paper, we propose to
learn the distance function directly on the manifold without embedding. We
first provide a theoretical characterization of the distance function by its
gradient field. Based on our theoretical analysis, we propose to first learn
the gradient field of the distance function and then learn the distance
function itself. Specifically, we set the gradient field of a local distance
function as an initial vector field. Then we transport it to the whole manifold
via heat flow on vector fields. Finally, the geodesic distance function can be
obtained by requiring its gradient field to be close to the normalized vector
field. Experimental results on both synthetic and real data demonstrate the
effectiveness of our proposed algorithm
深圳開展性工作者服務項目的困境與挑戰 = Problems and challenges in starting sex worker-oriented service projects in Shenzhen
A Dynamic Equivalent Energy Storage Model of Natural Gas Networks for Joint Optimal Dispatch of Electricity-Gas Systems
The development of energy conversion techniques enhances the coupling between
the gas network and power system. However, challenges remain in the joint
optimal dispatch of electricity-gas systems. The dynamic model of the gas
network, described by partial differential equations, is complex and
computationally demanding for power system operators. Furthermore, information
privacy concerns and limited accessibility to detailed gas network models by
power system operators necessitate quantifying the equivalent energy storage
capacity of gas networks. This paper proposes a multi-port energy storage model
with time-varying capacity to represent the dynamic gas state transformation
and operational constraints in a compact and intuitive form. The model can be
easily integrated into the optimal dispatch problem of the power system. Test
cases demonstrate that the proposed model ensures feasible control strategies
and significantly reduces the computational burden while maintaining high
accuracy in the joint optimal dispatch of electricity-gas systems. In contrast,
the existing static equivalent model fails to capture the full flexibility of
the gas network and may yield infeasible results.Comment: 12 pages, 8 figure
Novel glucose sensor based on enzymeimmobilized 81° tilted fiber grating
We demonstrate a novel glucose sensor based on an optical fiber grating with an excessively tilted index fringe structure and its surface modified by glucose oxidase (GOD). The aminopropyltriethoxysilane (APTES) was utilized as binding site for the subsequent GOD immobilization. Confocal microscopy and fluorescence microscope were used to provide the assessment of the effectiveness in modifying the fiber surface. The resonance wavelength of the sensor exhibited red-shift after the binding of the APTES and GOD to the fiber surface and also in the glucose detection process. The red-shift of the resonance wavelength showed a good linear response to the glucose concentration with a sensitivity of 0.298nm(mg/ml)-1 in the very low concentration range of 0.0∼3.0mg/ml. Compared to the previously reported glucose sensor based on the GOD-immobilized long period grating (LPG), the 81° tilted fiber grating (81°-TFG) based sensor has shown a lower thermal cross-talk effect, better linearity and higher Q-factor in sensing response. In addition, its sensitivity for glucose concentration can be further improved by increasing the grating length and/or choosing a higher-order cladding mode for detection. Potentially, the proposed techniques based on 81°-TFG can be developed as sensitive, label free and micro-structural sensors for applications in food safety, disease diagnosis, clinical analysis and environmental monitoring
Sensing the Pulse of the Pandemic: Geovisualizing the Demographic Disparities of Public Sentiment toward COVID-19 through Social Media
Social media offers a unique lens to observe users emotions and subjective
feelings toward critical events or topics and has been widely used to
investigate public sentiment during crises, e.g., the COVID-19 pandemic.
However, social media use varies across demographic groups, with younger people
being more inclined to use social media than the older population. This digital
divide could lead to biases in data representativeness and analysis results,
causing a persistent challenge in research based on social media data. This
study aims to tackle this challenge through a case study of estimating the
public sentiment about the COVID-19 using social media data. We analyzed the
pandemic-related Twitter data in the United States from January 2020 to
December 2021. The objectives are: (1) to elucidate the uneven social media
usage among various demographic groups and the disparities of their emotions
toward COVID-19, (2) to construct an unbiased measurement for public sentiment
based on social media data, the Sentiment Adjusted by Demographics (SAD) index,
through the post-stratification method, and (3) to evaluate the spatially and
temporally evolved public sentiment toward COVID-19 using the SAD index. The
results show significant discrepancies among demographic groups in their
COVID-19-related emotions. Female and under or equal to 18 years old Twitter
users expressed long-term negative sentiment toward COVID-19. The proposed SAD
index in this study corrected the underestimation of negative sentiment in 31
states, especially in Vermont. According to the SAD index, Twitter users in
Wyoming (Vermont) posted the largest (smallest) percentage of negative tweets
toward the pandemic
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