21 research outputs found
Will More Expressive Graph Neural Networks do Better on Generative Tasks?
Graph generation poses a significant challenge as it involves predicting a
complete graph with multiple nodes and edges based on simply a given label.
This task also carries fundamental importance to numerous real-world
applications, including de-novo drug and molecular design. In recent years,
several successful methods have emerged in the field of graph generation.
However, these approaches suffer from two significant shortcomings: (1) the
underlying Graph Neural Network (GNN) architectures used in these methods are
often underexplored; and (2) these methods are often evaluated on only a
limited number of metrics. To fill this gap, we investigate the expressiveness
of GNNs under the context of the molecular graph generation task, by replacing
the underlying GNNs of graph generative models with more expressive GNNs.
Specifically, we analyse the performance of six GNNs in two different
generative frameworks -- autoregressive generation models, such as GCPN and
GraphAF, and one-shot generation models, such as GraphEBM -- on six different
molecular generative objectives on the ZINC-250k dataset. Through our extensive
experiments, we demonstrate that advanced GNNs can indeed improve the
performance of GCPN, GraphAF, and GraphEBM on molecular generation tasks, but
GNN expressiveness is not a necessary condition for a good GNN-based generative
model. Moreover, we show that GCPN and GraphAF with advanced GNNs can achieve
state-of-the-art results across 17 other non-GNN-based graph generative
approaches, such as variational autoencoders and Bayesian optimisation models,
on the proposed molecular generative objectives (DRD2, Median1, Median2), which
are important metrics for de-novo molecular design.Comment: 2nd Learning on Graphs Conference (LoG 2023). 26 pages, 5 figures, 11
table
Observation of many-body Fock space dynamics in two dimensions
Quantum many-body simulation provides a straightforward way to understand
fundamental physics and connect with quantum information applications. However,
suffering from exponentially growing Hilbert space size, characterization in
terms of few-body probes in real space is often insufficient to tackle
challenging problems such as quantum critical behavior and many-body
localization (MBL) in higher dimensions. Here, we experimentally employ a new
paradigm on a superconducting quantum processor, exploring such elusive
questions from a Fock space view: mapping the many-body system onto an
unconventional Anderson model on a complex Fock space network of many-body
states. By observing the wave packet propagating in Fock space and the
emergence of a statistical ergodic ensemble, we reveal a fresh picture for
characterizing representative many-body dynamics: thermalization, localization,
and scarring. In addition, we observe a quantum critical regime of anomalously
enhanced wave packet width and deduce a critical point from the maximum wave
packet fluctuations, which lend support for the two-dimensional MBL transition
in finite-sized systems. Our work unveils a new perspective of exploring
many-body physics in Fock space, demonstrating its practical applications on
contentious MBL aspects such as criticality and dimensionality. Moreover, the
entire protocol is universal and scalable, paving the way to finally solve a
broader range of controversial many-body problems on future larger quantum
devices.Comment: 8 pages, 4 figures + supplementary informatio
Solar Ring Mission: Building a Panorama of the Sun and Inner-heliosphere
Solar Ring (SOR) is a proposed space science mission to monitor and study the
Sun and inner heliosphere from a full 360{\deg} perspective in the ecliptic
plane. It will deploy three 120{\deg}-separated spacecraft on the 1-AU orbit.
The first spacecraft, S1, locates 30{\deg} upstream of the Earth, the second,
S2, 90{\deg} downstream, and the third, S3, completes the configuration. This
design with necessary science instruments, e.g., the Doppler-velocity and
vector magnetic field imager, wide-angle coronagraph, and in-situ instruments,
will allow us to establish many unprecedented capabilities: (1) provide
simultaneous Doppler-velocity observations of the whole solar surface to
understand the deep interior, (2) provide vector magnetograms of the whole
photosphere - the inner boundary of the solar atmosphere and heliosphere, (3)
provide the information of the whole lifetime evolution of solar featured
structures, and (4) provide the whole view of solar transients and space
weather in the inner heliosphere. With these capabilities, Solar Ring mission
aims to address outstanding questions about the origin of solar cycle, the
origin of solar eruptions and the origin of extreme space weather events. The
successful accomplishment of the mission will construct a panorama of the Sun
and inner-heliosphere, and therefore advance our understanding of the star and
the space environment that holds our life.Comment: 41 pages, 6 figures, 1 table, to be published in Advances in Space
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The dynamic evolution of multipoint interplanetary coronal mass ejections observed with BepiColombo, Tianwen-1, and MAVEN
We present two multipoint interplanetary coronal mass ejections (ICMEs) detected by the Tianwen-1 and Mars Atmosphere and Volatile Evolution spacecraft at Mars and the BepiColombo (0.56 au âŒ0.67 au) upstream of Mars from 2021 December 5 to 31. This is the first time that BepiColombo is used as an upstream solar wind monitor ahead of Mars and that Tianwen-1 is used to investigate the magnetic field characteristics of ICMEs at Mars. The Heliospheric Upwind Extrapolation time model was used to connect the multiple in situ observations and the coronagraph observations from STEREO/SECCHI and SOHO/LASCO. The first fast coronal mass ejection event (âŒ761.2 km sâ1), which erupted on December 4, impacted Mars centrally and grazed BepiColombo by its western flank. The ambient slow solar wind decelerated the west flank of the ICME, implying that the ICME event was significantly distorted by the solar wind structure. The second slow ICME event (âŒ390.7 km sâ1) underwent an acceleration from its eruption to a distance within 0.69 au and then traveled with the constant velocity of the ambient solar wind. These findings highlight the importance of background solar wind in determining the interplanetary evolution and global morphology of ICMEs up to Mars distance. Observations from multiple locations are invaluable for space weather studies at Mars and merit more exploration in the future
Sedentary Behavior Estimation with Hip-worn Accelerometer Data: Segmentation, Classification and Thresholding
Cohort studies are increasingly using accelerometers for physical activity
and sedentary behavior estimation. These devices tend to be less error-prone
than self-report, can capture activity throughout the day, and are economical.
However, previous methods for estimating sedentary behavior based on hip-worn
data are often invalid or suboptimal under free-living situations and
subject-to-subject variation. In this paper, we propose a local Markov
switching model that takes this situation into account, and introduce a general
procedure for posture classification and sedentary behavior analysis that fits
the model naturally. Our method features changepoint detection methods in time
series and also a two stage classification step that labels data into 3
classes(sitting, standing, stepping). Through a rigorous training-testing
paradigm, we showed that our approach achieves > 80% accuracy. In addition, our
method is robust and easy to interpret
Monitoring of two-dimensional tungsten concentration profiles on the HL-2A tokamak
In this article, we demonstrate the inference of two-dimensional tungsten concentration profiles in tokamak plasmas, using Gaussian process tomography applied to bolometry and assuming a specific model for the tungsten cooling factor. In ITER, tungsten has been selected for divertor material due to its low tritium retention and ability to handle large heat and particle flux loads. On the other hand, this will cause tungsten impurities to enter the bulk plasma through various plasma-wall interaction processes. Therefore, a detailed understanding of tungsten impurity transport and active control of the impurity transport in tokamaks is crucial. The computational complexity of the method described in their article O(n(2)m) compares favorably to a simple least-squares approach O (n(3)), n represents the number of pixels and m the number of measurement channels, hence bringing real-time tungsten profile monitoring within reach (<10 ms repetition time). The feasibility study of this method has been demonstrated here to a discharge in HL-2A for observing the entire process of tungsten impurities entering the bulk plasma from the scrape-off layer area, tungsten pump-out by edge-localized modes, as well as the formation of a poloidally asymmetric tungsten distribution
Enhanced quantum state transfer by circumventing quantum chaotic behavior
Abstract The ability to realize high-fidelity quantum communication is one of the many facets required to build generic quantum computing devices. In addition to quantum processing, sensing, and storage, transferring the resulting quantum states demands a careful design that finds no parallel in classical communication. Existing experimental demonstrations of quantum information transfer in solid-state quantum systems are largely confined to small chains with few qubits, often relying upon non-generic schemes. Here, by using a superconducting quantum circuit featuring thirty-six tunable qubits, accompanied by general optimization procedures deeply rooted in overcoming quantum chaotic behavior, we demonstrate a scalable protocol for transferring few-particle quantum states in a two-dimensional quantum network. These include single-qubit excitation, two-qubit entangled states, and two excitations for which many-body effects are present. Our approach, combined with the quantum circuitâs versatility, paves the way to short-distance quantum communication for connecting distributed quantum processors or registers, even if hampered by inherent imperfections in actual quantum devices
Martian Bow Shock Oscillations Driven by Solar Wind Variations: Simultaneous Observations From Tianwenâ1 and MAVEN
International audienceThe Martian bow shock stands as the first defense against the solar wind and shapes the Martian magnetosphere. Previous studies showed the correlation between the Martian bow shock location and solar wind parameters. Here we present direct evidence of solar wind effects on the Martian bow shock by analyzing Tianwenâ1 and MAVEN data. We examined three cases where Tianwenâ1 data show rapid oscillations of the bow shock, while MAVEN data record changes in solar wind plasma and magnetic field. The results indicate that the bow shock is rapidly compressed and then expanded during the dynamic pressure pulse in the solar wind, and is also oscillated during the IMF rotation. The superposition of variations in multiple solar wind parameters leads to more intensive bow shock oscillation. This study emphasizes the importance of joint observations by Tianwenâ1 and MAVEN for studying the realâtime response of the Martian magnetosphere to the solar wind