126 research outputs found
When can we reconstruct the ancestral state? Beyond Brownian motion
Reconstructing the ancestral state of a group of species helps answer many
important questions in evolutionary biology. Therefore, it is crucial to
understand when we can estimate the ancestral state accurately. Previous works
provide a necessary and sufficient condition, called the big bang condition,
for the existence of an accurate reconstruction method under discrete trait
evolution models and the Brownian motion model. In this paper, we extend this
result to a wide range of continuous trait evolution models. In particular, we
consider a general setting where continuous traits evolve along the tree
according to stochastic processes that satisfy some regularity conditions. We
verify these conditions for popular continuous trait evolution models including
Ornstein-Uhlenbeck, reflected Brownian Motion, and Cox-Ingersoll-Ross
Spectral and Energy Efficiency Maximization for Content-Centric C-RANs with Edge Caching
This paper aims to maximize the spectral and energy efficiencies of a content-centric cloud radio access network (C-RAN), where users requesting the same contents are grouped together. Data are transferred from a central baseband unit to multiple remote radio heads (RRHs) equipped with local caches. The RRHs then send the received data to each group's user. Both multicast and unicast schemes are considered for data transmission. We formulate mixed-integer nonlinear problems in which user association, RRH activation, data rate allocation, and signal precoding are jointly designed. These challenging problems are subject to minimum data rate requirements, limited fronthaul capacity, and maximum RRH transmit power. Employing successive convex quadratic programming, we propose iterative algorithms with guaranteed convergence to Fritz John solutions. Numerical results confirm that the proposed joint designs markedly improve the spectral and energy efficiencies of the considered content-centric C-RAN compared to benchmark schemes. Importantly, they show that unicasting outperforms multicasting in terms of spectral efficiency in both cache and cache-less scenarios. In terms of energy efficiency, multicasting is the best choice for the system without cache whereas unicasting is best for the system with cache. Finally, edge caching is shown to improve both spectral and energy efficiencies.This work is supported in part by an ECRHDR scholarship from The University of Newcastle, in part by the Australian Research Council Discovery Project grants DP170100939 and DP160101537
Proportional green time scheduling for traffic lights
We consider the decentralized scheduling of a large number of urban traffic lights. We investigate factors determining system performance, in particular, the length of the traffic light cycle and the proportion of green time allocated to each junction. We study the effect of the length of the traffic cycle on the stability region a urban traffic network. We derive a simple square-root cycle length rule which is optimal for certain road traffic junctions. We prove the maximal stability of a road network under a proportional fair or P0 control scheme.
Further, we support of analysis through a simulation analysis of our policy on the Melbourne CBD urban road network
Energy-Efficient Design for Downlink Cloud Radio Access Networks
This work aims to maximize the energy efficiency of a downlink cloud radio access network (C-RAN), where data is transferred from a baseband unit in the core network to several remote radio heads via a set of edge routers over capacity-limited fronthaul links. The remote radio heads then send the received signals to their users via radio access links. We formulate a new mixed-integer nonlinear problem in which the ratio of network throughput and total power consumption is maximized. This challenging problem formulation includes practical constraints on routing, predefined minimum data rates, fronthaul capacity and maximum RRH transmit power. By employing the successive convex quadratic programming framework, an iterative algorithm is proposed with guaranteed convergence to a Fritz John solution of the formulated problem. Significantly, each iteration of the proposed algorithm solves only one simple convex program. Numerical examples with practical parameters confirm that the proposed joint optimization design markedly improves the C-RAN's energy efficiency compared to benchmark schemes.This work is supported in part by an ECR-HDR scholarship
from The University of Newcastle, in part by the Australian
Research Council Discovery Project grants DP170100939 and
DP160101537, in part by Vietnam National Foundation for
Science and Technology Development under grant number
101.02-2016.11 and in part by a startup fund from San Diego
State University
User Selection Approaches to Mitigate the Straggler Effect for Federated Learning on Cell-Free Massive MIMO Networks
This work proposes UE selection approaches to mitigate the straggler effect
for federated learning (FL) on cell-free massive multiple-input multiple-output
networks. To show how these approaches work, we consider a general FL framework
with UE sampling, and aim to minimize the FL training time in this framework.
Here, training updates are (S1) broadcast to all the selected UEs from a
central server, (S2) computed at the UEs sampled from the selected UE set, and
(S3) sent back to the central server. The first approach mitigates the
straggler effect in both Steps (S1) and (S3), while the second approach only
Step (S3). Two optimization problems are then formulated to jointly optimize UE
selection, transmit power and data rate. These mixed-integer mixed-timescale
stochastic nonconvex problems capture the complex interactions among the
training time, the straggler effect, and UE selection. By employing the online
successive convex approximation approach, we develop a novel algorithm to solve
the formulated problems with proven convergence to the neighbourhood of their
stationary points. Numerical results confirm that our UE selection designs
significantly reduce the training time over baseline approaches, especially in
the networks that experience serious straggler effects due to the moderately
low density of access points.Comment: submitted for peer review
Simple Transferability Estimation for Regression Tasks
We consider transferability estimation, the problem of estimating how well
deep learning models transfer from a source to a target task. We focus on
regression tasks, which received little previous attention, and propose two
simple and computationally efficient approaches that estimate transferability
based on the negative regularized mean squared error of a linear regression
model. We prove novel theoretical results connecting our approaches to the
actual transferability of the optimal target models obtained from the transfer
learning process. Despite their simplicity, our approaches significantly
outperform existing state-of-the-art regression transferability estimators in
both accuracy and efficiency. On two large-scale keypoint regression
benchmarks, our approaches yield 12% to 36% better results on average while
being at least 27% faster than previous state-of-the-art methods.Comment: Paper published at The 39th Conference on Uncertainty in Artificial
Intelligence (UAI) 202
On how religions could accidentally incite lies and violence: folktales as a cultural transmitter
Folklore has a critical role as a cultural transmitter, all the while being a socially accepted medium for the expressions of culturally contradicting wishes and conducts. In this study of Vietnamese folktales, through the use of Bayesian multilevel modeling and the Markov chain Monte Carlo technique, we offer empirical evidence for how the interplay between religious teachings (Confucianism, Buddhism, and Taoism) and deviant behaviors (lying and violence) could affect a folktale’s outcome. The findings indicate that characters who lie and/or commit violent acts tend to have bad endings, as intuition would dictate, but when they are associated with any of the above Three Teachings, the final endings may vary. Positive outcomes are seen in cases where characters associated with Confucianism lie and characters associated with Buddhism act violently. The results supplement the worldwide literature on discrepancies between folklore and real-life conduct, as well as on the contradictory human behaviors vis-à-vis religious teachings. Overall, the study highlights the complexity of human decision-making, especially beyond the folklore realm
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