579 research outputs found
On the validity of the definition of angular momentum in general relativity
We exam the validity of the definition of the ADM angular momentum without
the parity assumption. Explicit examples of asymptotically flat hypersurfaces
in the Minkowski spacetime with zero ADM energy-momentum vector and finite
non-zero angular momentum vector are presented. We also discuss the Beig-\'O
Murchadha-Regge-Teitelboim center of mass and study analogous examples in the
Schwarzschild spacetime.Comment: References are updated, and typos and computational errors are
corrected. Accepted by Ann. Henri Poincar
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Use electrochemistry to charge the next dynamic thermal metamaterials
Electrochemistry has enabled a wide range of important energy technologies such as fuel cells and batteries, emerging as a powerful tool to achieve active materials and devices with novel applications. In this Perspective, we highlight the great potential of electrochemistry in propelling the next generation of dynamic thermal metamaterials with a focus on thermal radiation applications. After a brief introduction of the mechanisms of electrochemistry to change material properties, we discuss the possibilities of achieving highly tunable thermal radiation features by electrochemically manipulating the carrier densities of plasmonic materials. Recent studies in the intersections between electrochemistry, metamaterials, and thermal radiation applications are reviewed, indicating an emerging research direction incorporating these three fields — electrochemically dynamic thermal metamaterials. Towards this direction, we anticipate a promising pathway of employing conducting polymers and point out its remarkable opportunities and potential challenges. We hope this perspective could encourage more researchers to contribute to the development of this interdisciplinary field targeting the next energy technologies and applications
Measuring Higher-Order Rationality with Belief Control
Determining an individual's strategic reasoning capability based solely on
choice data is a complex task. This complexity arises because sophisticated
players might have non-equilibrium beliefs about others, leading to
non-equilibrium actions. In our study, we pair human participants with computer
players known to be fully rational. This use of robot players allows us to
disentangle limited reasoning capacity from belief formation and social biases.
Our results show that, when paired with robots, subjects consistently
demonstrate higher levels of rationality and maintain stable rationality levels
across different games compared to when paired with humans. This suggests that
strategic reasoning might indeed be a consistent trait in individuals.
Furthermore, the identified rationality limits could serve as a measure for
evaluating an individual's strategic capacity when their beliefs about others
are adequately controlled.Comment: The experimental design and the analysis plan are pre-registered on
Open Science Framework (https://osf.io/gye4u/). The experimental instructions
can be found at https://mjfong.github.io/SI_MHOR_final.pd
Shared Representational Geometry Across Neural Networks
Different neural networks trained on the same dataset often learn similar
input-output mappings with very different weights. Is there some correspondence
between these neural network solutions? For linear networks, it has been shown
that different instances of the same network architecture encode the same
representational similarity matrix, and their neural activity patterns are
connected by orthogonal transformations. However, it is unclear if this holds
for non-linear networks. Using a shared response model, we show that different
neural networks encode the same input examples as different orthogonal
transformations of an underlying shared representation. We test this claim
using both standard convolutional neural networks and residual networks on
CIFAR10 and CIFAR100.Comment: Integration of Deep Learning Theories workshop, NeurIPS 201
Enabling Factor Analysis on Thousand-Subject Neuroimaging Datasets
The scale of functional magnetic resonance image data is rapidly increasing
as large multi-subject datasets are becoming widely available and
high-resolution scanners are adopted. The inherent low-dimensionality of the
information in this data has led neuroscientists to consider factor analysis
methods to extract and analyze the underlying brain activity. In this work, we
consider two recent multi-subject factor analysis methods: the Shared Response
Model and Hierarchical Topographic Factor Analysis. We perform analytical,
algorithmic, and code optimization to enable multi-node parallel
implementations to scale. Single-node improvements result in 99x and 1812x
speedups on these two methods, and enables the processing of larger datasets.
Our distributed implementations show strong scaling of 3.3x and 5.5x
respectively with 20 nodes on real datasets. We also demonstrate weak scaling
on a synthetic dataset with 1024 subjects, on up to 1024 nodes and 32,768
cores
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A kirigami-enabled electrochromic wearable variable-emittance device for energy-efficient adaptive personal thermoregulation
For centuries, people have put effort to improve the thermal performance of clothing to adapt to varying temperatures. However, most clothing we wear today only offers a single-mode insulation. The adoption of active thermal management devices, such as resistive heaters, Peltier coolers, and water recirculation, is limited by their excessive energy consumption and form factor for long-term, continuous, and personalized thermal comfort. In this paper, we developed a wearable variable-emittance (WeaVE) device, enabling the tunable radiative heat transfer coefficient to fill the missing gap between thermoregulation energy efficiency and controllability. WeaVE is an electrically driven, kirigami-enabled electrochromic thin-film device that can effectively tune the midinfrared thermal radiation heat loss of the human body. The kirigami design provides stretchability and conformal deformation under various modes and exhibits excellent mechanical stability after 1,000 cycles. The electronic control enables programmable personalized thermoregulation. With less than 5.58 mJ/cm2 energy input per switching, WeaVE provides 4.9°C expansion of the thermal comfort zone, which is equivalent to a continuous power input of 33.9 W/m2. This nonvolatile characteristic substantially decreases the required energy while maintaining the on-demand controllability, thereby providing vast opportunities for the next generation of smart personal thermal managing fabrics and wearable technologies
TAG: Learning Circuit Spatial Embedding From Layouts
Analog and mixed-signal (AMS) circuit designs still rely on human design
expertise. Machine learning has been assisting circuit design automation by
replacing human experience with artificial intelligence. This paper presents
TAG, a new paradigm of learning the circuit representation from layouts
leveraging text, self-attention and graph. The embedding network model learns
spatial information without manual labeling. We introduce text embedding and a
self-attention mechanism to AMS circuit learning. Experimental results
demonstrate the ability to predict layout distances between instances with
industrial FinFET technology benchmarks. The effectiveness of the circuit
representation is verified by showing the transferability to three other
learning tasks with limited data in the case studies: layout matching
prediction, wirelength estimation, and net parasitic capacitance prediction.Comment: Accepted by ICCAD 202
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