276 research outputs found
A study on fault diagnosis in nonlinear dynamic systems with uncertainties
In this draft, fault diagnosis in nonlinear dynamic systems is addressed. The
objective of this work is to establish a framework, in which not only
model-based but also data-driven and machine learning based fault diagnosis
strategies can be uniformly handled. Instead of the well-established
input-output and the associated state space models, stable image and kernel
representations are adopted in our work as the basic process model forms. Based
on it, the nominal system dynamics can then be modelled as a lower-dimensional
manifold embedded in the process data space. To achieve a reliable fault
detection as a classification problem, projection technique is a capable tool.
For nonlinear dynamic systems, we propose to construct projection systems in
the well-established framework of Hamiltonian systems and by means of the
normalised image and kernel representations. For nonlinear dynamic systems,
process data form a non-Euclidean space. Consequently, the norm-based distance
defined in Hilbert space is not suitable to measure the distance from a data
vector to the manifold of the nominal dynamics. To deal with this issue, we
propose to use a Bregman divergence, a measure of difference between two points
in a space, as a solution. Moreover, for our purpose of achieving a
performance-oriented fault detection, the Bregman divergences adopted in our
work are defined by Hamiltonian functions. This scheme not only enables to
realise the performance-oriented fault detection, but also uncovers the
information geometric aspect of our work. The last part of our work is devoted
to the kernel representation based fault detection and uncertainty estimation
that can be equivalently used for fault estimation. It is demonstrated that the
projection onto the manifold of uncertainty data, together with the
correspondingly defined Bregman divergence, is also capable for fault
detection
Control theoretically explainable application of autoencoder methods to fault detection in nonlinear dynamic systems
This paper is dedicated to control theoretically explainable application of
autoencoders to optimal fault detection in nonlinear dynamic systems.
Autoencoder-based learning is a standard method of machine learning technique
and widely applied for fault (anomaly) detection and classification. In the
context of representation learning, the so-called latent (hidden) variable
plays an important role towards an optimal fault detection. In ideal case, the
latent variable should be a minimal sufficient statistic. The existing
autoencoder-based fault detection schemes are mainly application-oriented, and
few efforts have been devoted to optimal autoencoder-based fault detection and
explainable applications. The main objective of our work is to establish a
framework for learning autoencoder-based optimal fault detection in nonlinear
dynamic systems. To this aim, a process model form for dynamic systems is
firstly introduced with the aid of control and system theory, which also leads
to a clear system interpretation of the latent variable. The major efforts are
devoted to the development of a control theoretical solution to the optimal
fault detection problem, in which an analog concept to minimal sufficient
statistic, the so-called lossless information compression, is introduced for
dynamic systems and fault detection specifications. In particular, the
existence conditions for such a latent variable are derived, based on which a
loss function and further a learning algorithm are developed. This learning
algorithm enables optimally training of autoencoders to achieve an optimal
fault detection in nonlinear dynamic systems. A case study on three-tank system
is given at the end of this paper to illustrate the capability of the proposed
autoencoder-based fault detection and to explain the essential role of the
latent variable in the proposed fault detection system
Replay Attack Detection Based on Parity Space Method for Cyber-Physical Systems
The replay attack detection problem is studied from a new perspective based
on parity space method in this paper. The proposed detection methods have the
ability to distinguish system fault and replay attack, handle both input and
output data replay, maintain certain control performance, and can be
implemented conveniently and efficiently. First, the replay attack effect on
the residual is derived and analyzed. The residual change induced by replay
attack is characterized explicitly and the detection performance analysis based
on two different test statistics are given. Second, based on the replay attack
effect characterization, targeted passive and active design for detection
performance enhancement are proposed. Regarding the passive design, four
optimization schemes regarding different cost functions are proposed with
optimal parity matrix solutions, and the unified solution to the passive
optimization schemes is obtained; the active design is enabled by a marginally
stable filter so as to enlarge the replay attack effect on the residual for
detection. Simulations and comparison studies are given to show the
effectiveness of the proposed methods
Identification of plasma lipid biomarkers for prostate cancer by lipidomics and bioinformatics
Background:
Lipids have critical functions in cellular energy storage, structure and signaling. Many individual lipid molecules have been associated with the evolution of prostate cancer; however, none of them has been approved to be used as a biomarker. The aim of this study is to identify lipid molecules from hundreds plasma apparent lipid species as biomarkers for diagnosis of prostate cancer.
Methodology/Principal Findings:
Using lipidomics, lipid profiling of 390 individual apparent lipid species was performed on 141 plasma samples from 105 patients with prostate cancer and 36 male controls. High throughput data generated from lipidomics were analyzed using bioinformatic and statistical methods. From 390 apparent lipid species, 35 species were demonstrated to have potential in differentiation of prostate cancer. Within the 35 species, 12 were identified as individual plasma lipid biomarkers for diagnosis of prostate cancer with a sensitivity above 80%, specificity above 50% and accuracy above 80%. Using top 15 of 35 potential biomarkers together increased predictive power dramatically in diagnosis of prostate cancer with a sensitivity of 93.6%, specificity of 90.1% and accuracy of 97.3%. Principal component analysis (PCA) and hierarchical clustering analysis (HCA) demonstrated that patient and control populations were visually separated by identified lipid biomarkers. RandomForest and 10-fold cross validation analyses demonstrated that the identified lipid biomarkers were able to predict unknown populations accurately, and this was not influenced by patient's age and race. Three out of 13 lipid classes, phosphatidylethanolamine (PE), ether-linked phosphatidylethanolamine (ePE) and ether-linked phosphatidylcholine (ePC) could be considered as biomarkers in diagnosis of prostate cancer.
Conclusions/Significance:
Using lipidomics and bioinformatic and statistical methods, we have identified a few out of hundreds plasma apparent lipid molecular species as biomarkers for diagnosis of prostate cancer with a high sensitivity, specificity and accuracy
Experimental evaluation of the importance of colonization history in early-life gut microbiota assembly
The factors that govern assembly of the gut microbiota are insufficiently understood. Here, we test the hypothesis that inter-individual microbiota variation can arise solely from differences in the order and timing by which the gut is colonized early in life. Experiments in which mice were inoculated in sequence either with two complex seed communities or a cocktail of four bacterial strains and a seed community revealed that colonization order influenced both the outcome of community assembly and the ecological success of individual colonizers. Historical contingency and priority effects also occurred in Rag1-/- mice, suggesting that the adaptive immune system is not a major contributor to these processes. In conclusion, this study established a measurable effect of colonization history on gut microbiota assembly in a model in which host and environmental factors were strictly controlled, illuminating a potential cause for the high levels of unexplained individuality in host-associated microbial communities.
Supplemental figures attached below
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