636 research outputs found
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The Aging Heart: Mitophagy at the Center of Rejuvenation.
Aging is associated with structural and functional changes in the heart and is a major risk factor in developing cardiovascular disease. Many recent studies have focused on increasing our understanding of the basis of aging at the cellular and molecular levels in various tissues, including the heart. It is known that there is an age-related decline in cellular quality control pathways such as autophagy and mitophagy, which leads to accumulation of potentially harmful cellular components in cardiac myocytes. There is evidence that diminished autophagy and mitophagy accelerate the aging process, while enhancement preserves cardiac homeostasis and extends life span. Here, we review the current knowledge of autophagy and mitophagy in aging and discuss how age-associated alterations in these processes contribute to cardiac aging and age-related cardiovascular diseases
Attitude Estimation of Quadcopter through Extended Kalman Filter
The aim of this paper is to estimate the attitude of the quadcopter using the sensors: 3-axesaccelerometer, 3-axes gyroscope, 2-axes compass.At first I introduce some basic conception of quadcopter, such as the three main factor: roll, pitch,yaw, and the coordinate system that are used to implement the next calculations. Then according tothe mathematical model, I simulated the quadcopter in Simulink. The sensors are also modeled usingthe real sensor measurements to correctly estimate the measurement noise.After finished the model, I gave it a step input and get the output from the scope. Then I add theGaussian noise on to it and use this as the input of Extended Kalman Filter. And compare somedifferent type of Kalman Filter to conclude that the EKF is the best strategy.Finally we can conclude that the standard extended Kalman filter is the best estimator. If allof the parameters can be set correctly, The EKF can have a better result. But since it is notimplement on the embedded system, it can be used only as a reference and provide satisfyingresult in most situations.Keywords: Quadcopter, Extended Kalman Filter, Eular angl
Channel Estimation for Ambient Backscatter Communication Systems with Massive-Antenna Reader
Ambient backscatter, an emerging green communication technology, has aroused
great interest from both academia and industry. One open problem for ambient
backscatter communication (AmBC) systems is channel estimation for a
massive-antenna reader. In this paper, we focus on channel estimation problem
in AmBC systems with uniform linear array (ULA) at the reader which consists of
large number of antennas. We first design a two-step method to jointly estimate
channel gains and direction of arrivals (DoAs), and then refine the estimates
through angular rotation. Additionally, Cramer-Rao lower bounds (CRLBs) are
derived for both the modulus of the channel gain and the DoA estimates.
Simulations are then provided to validate the analysis, and to show the
efficiency of the proposed approach.Comment: 5 figures, submitted to IEEE Transactions on Vehicular Technology, 29
March, 201
Momentum and Mass Fluxes in a Gas Confined between Periodically Structured Surfaces at Different Temperatures
It is well known that in a gas-filled duct or channel along which a
temperature gradient is applied, a thermal creep flow is created. Here we show
that a mass and momentum flux can also be induced in a gas confined between two
parallel structured surfaces at different temperatures, i.e.
\textit{orthogonal} to the temperature gradient. We use both analytical and
numerical methods to compute the resulting fluxes. The momentum flux assumes
its maximum value in the free-molecular flow regime, the (normalized) mass flux
in the transition flow regime. The discovered phenomena could find applications
in novel methods for energy-conversion and thermal pumping of gases.Comment: 6 pages, 5 figures, updated fig.5, updated text for the numerical
metho
Verifying Safety of Neural Networks from Topological Perspectives
Neural networks (NNs) are increasingly applied in safety-critical systems
such as autonomous vehicles. However, they are fragile and are often
ill-behaved. Consequently, their behaviors should undergo rigorous guarantees
before deployment in practice. In this paper, we propose a set-boundary
reachability method to investigate the safety verification problem of NNs from
a topological perspective. Given an NN with an input set and a safe set, the
safety verification problem is to determine whether all outputs of the NN
resulting from the input set fall within the safe set. In our method, the
homeomorphism property and the open map property of NNs are mainly exploited,
which establish rigorous guarantees between the boundaries of the input set and
the boundaries of the output set. The exploitation of these two properties
facilitates reachability computations via extracting subsets of the input set
rather than the entire input set, thus controlling the wrapping effect in
reachability analysis and facilitating the reduction of computation burdens for
safety verification. The homeomorphism property exists in some widely used NNs
such as invertible residual networks (i-ResNets) and Neural ordinary
differential equations (Neural ODEs), and the open map is a less strict
property and easier to satisfy compared with the homeomorphism property. For
NNs establishing either of these properties, our set-boundary reachability
method only needs to perform reachability analysis on the boundary of the input
set. Moreover, for NNs that do not feature these properties with respect to the
input set, we explore subsets of the input set for establishing the local
homeomorphism property and then abandon these subsets for reachability
computations. Finally, some examples demonstrate the performance of the
proposed method.Comment: 25 pages, 11 figures. arXiv admin note: substantial text overlap with
arXiv:2210.0417
Safety Verification for Neural Networks Based on Set-boundary Analysis
Neural networks (NNs) are increasingly applied in safety-critical systems
such as autonomous vehicles. However, they are fragile and are often
ill-behaved. Consequently, their behaviors should undergo rigorous guarantees
before deployment in practice. In this paper we propose a set-boundary
reachability method to investigate the safety verification problem of NNs from
a topological perspective. Given an NN with an input set and a safe set, the
safety verification problem is to determine whether all outputs of the NN
resulting from the input set fall within the safe set. In our method, the
homeomorphism property of NNs is mainly exploited, which establishes a
relationship mapping boundaries to boundaries. The exploitation of this
property facilitates reachability computations via extracting subsets of the
input set rather than the entire input set, thus controlling the wrapping
effect in reachability analysis and facilitating the reduction of computation
burdens for safety verification. The homeomorphism property exists in some
widely used NNs such as invertible NNs. Notable representations are invertible
residual networks (i-ResNets) and Neural ordinary differential equations
(Neural ODEs). For these NNs, our set-boundary reachability method only needs
to perform reachability analysis on the boundary of the input set. For NNs
which do not feature this property with respect to the input set, we explore
subsets of the input set for establishing the local homeomorphism property, and
then abandon these subsets for reachability computations. Finally, some
examples demonstrate the performance of the proposed method.Comment: 19 pages, 7 figure
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