67 research outputs found
Learning Motion Predictors for Smart Wheelchair using Autoregressive Sparse Gaussian Process
Constructing a smart wheelchair on a commercially available powered
wheelchair (PWC) platform avoids a host of seating, mechanical design and
reliability issues but requires methods of predicting and controlling the
motion of a device never intended for robotics. Analog joystick inputs are
subject to black-box transformations which may produce intuitive and adaptable
motion control for human operators, but complicate robotic control approaches;
furthermore, installation of standard axle mounted odometers on a commercial
PWC is difficult. In this work, we present an integrated hardware and software
system for predicting the motion of a commercial PWC platform that does not
require any physical or electronic modification of the chair beyond plugging
into an industry standard auxiliary input port. This system uses an RGB-D
camera and an Arduino interface board to capture motion data, including visual
odometry and joystick signals, via ROS communication. Future motion is
predicted using an autoregressive sparse Gaussian process model. We evaluate
the proposed system on real-world short-term path prediction experiments.
Experimental results demonstrate the system's efficacy when compared to a
baseline neural network model.Comment: The paper has been accepted to the International Conference on
Robotics and Automation (ICRA2018
Front-running Attack in Sharded Blockchains and Fair Cross-shard Consensus
Sharding is a prominent technique for scaling blockchains. By dividing the
network into smaller components known as shards, a sharded blockchain can
process transactions in parallel without introducing inconsistencies through
the coordination of intra-shard and cross-shard consensus protocols. However,
we observe a critical security issue with sharded systems: transaction ordering
manipulations can occur when coordinating intra-shard and cross-shard consensus
protocols, leaving the system vulnerable to attack. Specifically, we identify a
novel security issue known as finalization fairness, which can be exploited
through a front-running attack. This attack allows an attacker to manipulate
the execution order of transactions, even if the victim's transaction has
already been processed and added to the blockchain by a fair intra-shard
consensus.
To address the issue, we offer Haechi, a novel cross-shard protocol that is
immune to front-running attacks. Haechi introduces an ordering phase between
transaction processing and execution, ensuring that the execution order of
transactions is the same as the processing order and achieving finalization
fairness. To accommodate different consensus speeds among shards, Haechi
incorporates a finalization fairness algorithm to achieve a globally fair order
with minimal performance loss. By providing a global order, Haechi ensures
strong consistency among shards, enabling better parallelism in handling
conflicting transactions across shards. These features make Haechi a promising
solution for supporting popular smart contracts in the real world. To evaluate
Haechi's performance, we implemented the protocol using Tendermint and
conducted extensive experiments on a geo-distributed AWS environment. Our
results demonstrate that Haechi achieves finalization fairness with little
performance sacrifice compared to existing cross-shard consensus protocols
Compassion, Discrimination, and Prosocial Behaviors: Young Diasporic Chinese During the COVID-19 Pandemic
The coronavirus disease 2019 (COVID-19) pandemic has fueled anti-Asian, especially anti-Chinese sentiments worldwide, which may negatively impact diasporic Chinese youths\u27 adjustment and prosocial development. This study examined the association between compassion, discrimination and prosocial behaviors in diasporic Chinese youths during the COVID-19 pandemic. 360 participants participated and completed the multi-country, cross-sectional, web-based survey between April 22 and May 9, 2020, the escalating stage of the pandemic. This study found compassion as prosocial behaviors\u27 proximal predictor, while discrimination independently predicted participation in volunteering, and could potentially enhance the association between compassion and charitable giving. These findings suggest that prosociality among young people is sensitive to social context, and that racial discrimination should be considered in future prosocial studies involving young members of ethnic and racial minorities
Prophet: Conflict-Free Sharding Blockchain via Byzantine-Tolerant Deterministic Ordering
Sharding scales throughput by splitting blockchain nodes into parallel
groups. However, different shards' independent and random scheduling for
cross-shard transactions results in numerous conflicts and aborts, since
cross-shard transactions from different shards may access the same account. A
deterministic ordering can eliminate conflicts by determining a global order
for transactions before processing, as proved in the database field.
Unfortunately, due to the intertwining of the Byzantine environment and
information isolation among shards, there is no trusted party able to
predetermine such an order for cross-shard transactions. To tackle this
challenge, this paper proposes Prophet, a conflict-free sharding blockchain
based on Byzantine-tolerant deterministic ordering. It first depends on
untrusted self-organizing coalitions of nodes from different shards to
pre-execute cross-shard transactions for prerequisite information about
ordering. It then determines a trusted global order based on stateless ordering
and post-verification for pre-executed results, through shard cooperation.
Following the order, the shards thus orderly execute and commit transactions
without conflicts. Prophet orchestrates the pre-execution, ordering, and
execution processes in the sharding consensus for minimal overhead. We
rigorously prove the determinism and serializability of transactions under the
Byzantine and sharded environment. An evaluation of our prototype shows that
Prophet improves the throughput by and achieves nearly no aborts
on 1 million Ethereum transactions compared with state-of-the-art sharding
HOLD: Category-agnostic 3D Reconstruction of Interacting Hands and Objects from Video
Since humans interact with diverse objects every day, the holistic 3D capture
of these interactions is important to understand and model human behaviour.
However, most existing methods for hand-object reconstruction from RGB either
assume pre-scanned object templates or heavily rely on limited 3D hand-object
data, restricting their ability to scale and generalize to more unconstrained
interaction settings. To this end, we introduce HOLD -- the first
category-agnostic method that reconstructs an articulated hand and object
jointly from a monocular interaction video. We develop a compositional
articulated implicit model that can reconstruct disentangled 3D hand and object
from 2D images. We also further incorporate hand-object constraints to improve
hand-object poses and consequently the reconstruction quality. Our method does
not rely on 3D hand-object annotations while outperforming fully-supervised
baselines in both in-the-lab and challenging in-the-wild settings. Moreover, we
qualitatively show its robustness in reconstructing from in-the-wild videos.
Code: https://github.com/zc-alexfan/hol
Experimental and numerical investigation of a novel photovoltaic/thermal system using micro-channel flat loop heat pipe (PV/T-MCFLHP)
In this paper, a novel photovoltaic/thermal system using micro-channel flat loop heat pipe (PV/T-MCFLHP) is proposed, and the thermal and electrical performance of the system is investigated theoretically and experimentally. The variations of temperatures were analysed, and the efficiency of the system was calculated under different conditions, i.e. simulated solar radiation, water flow rate and refrigerant filling ratio. The maximum overall efficiency of the system was found to be 51.3%, the thermal efficiency 43.8% and the electrical efficiency 7.5% with the refrigerant filling ratio of 25%, simulated solar radiation of 800 W/m2 and water flow rate of 400 L/h. Test results were compared with simulation results, and the recorded average error was 10.2%
Improving hindlimb locomotor function by non-invasive AAV-mediated manipulations of propriospinal neurons in mice with complete spinal cord injury
After complete spinal cord injury, spinal segments below the lesion maintain inter-segmental communication via the intraspinal propriospinal network. Here, the authors show that neurons in these circuits can be chemogenetically modulated to improve locomotor function in mice after spinal cord injury
Prediction of myopia development among Chinese school-aged children using refraction data from electronic medical records: A retrospective, multicentre machine learning study
Background
Electronic medical records provide large-scale real-world clinical data for use in developing clinical decision systems. However, sophisticated methodology and analytical skills are required to handle the large-scale datasets necessary for the optimisation of prediction accuracy. Myopia is a common cause of vision loss. Current approaches to control myopia progression are effective but have significant side effects. Therefore, identifying those at greatest risk who should undergo targeted therapy is of great clinical importance. The objective of this study was to apply big data and machine learning technology to develop an algorithm that can predict the onset of high myopia, at specific future time points, among Chinese school-aged children.
Methods and findings
Real-world clinical refraction data were derived from electronic medical record systems in 8 ophthalmic centres from January 1, 2005, to December 30, 2015. The variables of age, spherical equivalent (SE), and annual progression rate were used to develop an algorithm to predict SE and onset of high myopia (SE ≤ −6.0 dioptres) up to 10 years in the future. Random forest machine learning was used for algorithm training and validation. Electronic medical records from the Zhongshan Ophthalmic Centre (a major tertiary ophthalmic centre in China) were used as the training set. Ten-fold cross-validation and out-of-bag (OOB) methods were applied for internal validation. The remaining 7 independent datasets were used for external validation. Two population-based datasets, which had no participant overlap with the ophthalmic-centre-based datasets, were used for multi-resource validation testing. The main outcomes and measures were the area under the curve (AUC) values for predicting the onset of high myopia over 10 years and the presence of high myopia at 18 years of age. In total, 687,063 multiple visit records (≥3 records) of 129,242 individuals in the ophthalmic-centre-based electronic medical record databases and 17,113 follow-up records of 3,215 participants in population-based cohorts were included in the analysis. Our algorithm accurately predicted the presence of high myopia in internal validation (the AUC ranged from 0.903 to 0.986 for 3 years, 0.875 to 0.901 for 5 years, and 0.852 to 0.888 for 8 years), external validation (the AUC ranged from 0.874 to 0.976 for 3 years, 0.847 to 0.921 for 5 years, and 0.802 to 0.886 for 8 years), and multi-resource testing (the AUC ranged from 0.752 to 0.869 for 4 years). With respect to the prediction of high myopia development by 18 years of age, as a surrogate of high myopia in adulthood, the algorithm provided clinically acceptable accuracy over 3 years (the AUC ranged from 0.940 to 0.985), 5 years (the AUC ranged from 0.856 to 0.901), and even 8 years (the AUC ranged from 0.801 to 0.837). Meanwhile, our algorithm achieved clinically acceptable prediction of the actual refraction values at future time points, which is supported by the regressive performance and calibration curves. Although the algorithm achieved balanced and robust performance, concerns about the compromised quality of real-world clinical data and over-fitting issues should be cautiously considered.
Conclusions
To our knowledge, this study, for the first time, used large-scale data collected from electronic health records to demonstrate the contribution of big data and machine learning approaches to improved prediction of myopia prognosis in Chinese school-aged children. This work provides evidence for transforming clinical practice, health policy-making, and precise individualised interventions regarding the practical control of school-aged myopia.This study was funded by the National
Key R&D Program of China (2018YFC0116500),
the National Natural Science Foundation of China
(91546101, 81822010), the Guangdong Science
and Technology Innovation Leading Talents
(2017TX04R031), and Youth Pearl River Scholar in
Guangdong (2016)
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