52 research outputs found
Testing and selecting cosmological models with ultra-compact radio quasars
In this paper, we place constraints on four alternative cosmological models
under the assumption of the spatial flatness of the Universe: CPL, EDE, GCG and
MPC. A new compilation of 120 compact radio quasars observed by
very-long-baseline interferometry, which represents a type of new cosmological
standard rulers, are used to test these cosmological models. Our results show
that the fits on CPL obtained from the quasar sample are well consistent with
those obtained from BAO. For other cosmological models considered, quasars
provide constraints in agreement with those derived with other standard probes
at confidence level. Moreover, the results obtained from other
statistical methods including Figure of Merit, and statefinder
diagnostics indicate that: (1) Radio quasar standard ruler could provide better
statistical constraints than BAO for all cosmological models considered, which
suggests its potential to act as a powerful complementary probe to BAO and
galaxy clusters. (2) Turning to diagnostics, CPL, GCG and EDE models
can not be distinguished from each other at the present epoch. (3) In the
framework of statefinder diagnostics, MPC and EDE will deviate from
CDM model in the near future, while GCG model cannot be
distinguished from CDM model unless much higher precision
observations are available.Comment: 12 pages, 8 figures, 1 tabl
Online Control with Adversarial Disturbance for Continuous-time Linear Systems
We study online control for continuous-time linear systems with finite
sampling rates, where the objective is to design an online procedure that
learns under non-stochastic noise and performs comparably to a fixed optimal
linear controller. We present a novel two-level online algorithm, by
integrating a higher-level learning strategy and a lower-level feedback control
strategy. This method offers a practical and robust solution for online
control, which achieves sublinear regret. Our work provides one of the first
nonasymptotic results for controlling continuous-time linear systems a with
finite number of interactions with the system
Neural Network Weights Do Not Converge to Stationary Points: An Invariant Measure Perspective
This work examines the deep disconnect between existing theoretical analyses
of gradient-based algorithms and the practice of training deep neural networks.
Specifically, we provide numerical evidence that in large-scale neural network
training (e.g., ImageNet + ResNet101, and WT103 + TransformerXL models), the
neural network's weights do not converge to stationary points where the
gradient of the loss is zero. Remarkably, however, we observe that even though
the weights do not converge to stationary points, the progress in minimizing
the loss function halts and training loss stabilizes. Inspired by this
observation, we propose a new perspective based on ergodic theory of dynamical
systems to explain it. Rather than studying the evolution of weights, we study
the evolution of the distribution of weights. We prove convergence of the
distribution of weights to an approximate invariant measure, thereby explaining
how the training loss can stabilize without weights necessarily converging to
stationary points. We further discuss how this perspective can better align
optimization theory with empirical observations in machine learning practice
Iteratively Learn Diverse Strategies with State Distance Information
In complex reinforcement learning (RL) problems, policies with similar
rewards may have substantially different behaviors. It remains a fundamental
challenge to optimize rewards while also discovering as many diverse strategies
as possible, which can be crucial in many practical applications. Our study
examines two design choices for tackling this challenge, i.e., diversity
measure and computation framework. First, we find that with existing diversity
measures, visually indistinguishable policies can still yield high diversity
scores. To accurately capture the behavioral difference, we propose to
incorporate the state-space distance information into the diversity measure. In
addition, we examine two common computation frameworks for this problem, i.e.,
population-based training (PBT) and iterative learning (ITR). We show that
although PBT is the precise problem formulation, ITR can achieve comparable
diversity scores with higher computation efficiency, leading to improved
solution quality in practice. Based on our analysis, we further combine ITR
with two tractable realizations of the state-distance-based diversity measures
and develop a novel diversity-driven RL algorithm, State-based Intrinsic-reward
Policy Optimization (SIPO), with provable convergence properties. We
empirically examine SIPO across three domains from robot locomotion to
multi-agent games. In all of our testing environments, SIPO consistently
produces strategically diverse and human-interpretable policies that cannot be
discovered by existing baselines
Direct test of the FLRW metric from strongly lensed gravitational wave observations
The assumptions of large-scale homogeneity and isotropy underly the familiar Friedmann-Lemaître-
Robertson-Walker (FLRW) metric that appears to be an accurate description of our Universe. In this
paper, we propose a new strategy of testing the validity of the FLRW metric, based on the galactic-scale
lensing systems where strongly lensed gravitational waves and their electromagnetic counterparts
can be simultaneously detected. Each strong lensing system creates opportunity to infer the curvature
parameter of the Universe. Consequently, combined analysis of many such systems will provide a
model-independent tool to test the validity of the FLRW metric. Our study demonstrates that the thirdgeneration ground based GW detectors, like the Einstein Telescope (ET) and space-based detectors, like the Big Bang Observer (BBO), are promising concerning determination of the curvature parameter or possible detection of deviation from the FLRW metric. Such accurate measurements of the FLRW metric can become a milestone in precision GW cosmology
Early Identification and Diagnosis of Adrenal Crisis after Retroperitoneal Laparoscopic Unilateral Adrenalectomy
The occurrence of adrenal crisis after retroperitoneal laparoscopic unilateral adrenalectomy is usually concealed. If not timely diagnosis and treatment,it may cause shock, and even lead to death. It is very difficult to distinguish the clinical manifestations of adrenal crisis from nausea, vomiting, fatigue,gas separation from the lower diaphragm, abdominal pain, hypotension, hypertension, fever and hypothermia after operation. This makes it very difficult to identify and diagnose adrenal crisis early. This article mainly discusses the early recognition, diagnosis and treatment of adrenal crisis after unilateral adrenalectomy by retroperitoneoscope
In Situ Measurements of the Mechanical Properties of Electrochemically Deposited Li₂CO₃ and Li₂O Nanorods
Solid-electrolyte interface (SEI) is “the most important but least understood (component) in rechargeable Li-ion batteries”. The ideal SEI requires high elastic strength and can resist the penetration of a Li dendrite mechanically, which is vital for inhibiting the dendrite growth in lithium batteries. Even though LiCO and LiO are identified as the major components of SEI, their mechanical properties are not well understood. Herein, SEI-related materials such as LiCO and LiO were electrochemically deposited using an environmental transmission electron microscopy (ETEM), and their mechanical properties were assessed by in situ atomic force microscopy (AFM) and inverse finite element simulations. Both LiCO and LiO exhibit nanocrystalline structures and good plasticity. The ultimate strength of LiCO ranges from 192 to 330 MPa, while that of LiO is less than 100 MPa. These results provide a new understanding of the SEI and its related dendritic problems in lithium batteries
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