42,822 research outputs found
Profile control charts based on nonparametric -1 regression methods
Classical statistical process control often relies on univariate
characteristics. In many contemporary applications, however, the quality of
products must be characterized by some functional relation between a response
variable and its explanatory variables. Monitoring such functional profiles has
been a rapidly growing field due to increasing demands. This paper develops a
novel nonparametric -1 location-scale model to screen the shapes of
profiles. The model is built on three basic elements: location shifts, local
shape distortions, and overall shape deviations, which are quantified by three
individual metrics. The proposed approach is applied to the previously analyzed
vertical density profile data, leading to some interesting insights.Comment: Published in at http://dx.doi.org/10.1214/11-AOAS501 the Annals of
Applied Statistics (http://www.imstat.org/aoas/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Combination of statistical process control (SPC) methods and classification strategies for situation assessment of batch processes
Postprint (published version
On monitoring of multiple non-linear profiles
Most state-of-the-art profile monitoring methods involve studies of one profile. However, a process may contain several sensors or probes that generate multiple profiles over time. Quality characteristics presented in multiple profiles may be related multiple aspects of product or process quality. Existing charting methods for simultaneous monitoring of each multiple profile may result in high false alarm rates. Or worse, they cannot correctly detect potential relationship changes among profiles. In this study, we propose two approaches to detect process shifts in multiple non-linear profiles. A simulation study was conducted to evaluate the performance of the proposed approaches in terms of average run length under different process shift scenarios. Pros and cons of the proposed methods are discussed. A guideline for choosing the proposed methods is introduced. In addition, a hybrid method combining the salient points of both approaches is explored. Finally, a real-world data-set from a vulcanisation process is used to demonstrate the implementation of the proposed methods
Likelihood-informed dimension reduction for nonlinear inverse problems
The intrinsic dimensionality of an inverse problem is affected by prior
information, the accuracy and number of observations, and the smoothing
properties of the forward operator. From a Bayesian perspective, changes from
the prior to the posterior may, in many problems, be confined to a relatively
low-dimensional subspace of the parameter space. We present a dimension
reduction approach that defines and identifies such a subspace, called the
"likelihood-informed subspace" (LIS), by characterizing the relative influences
of the prior and the likelihood over the support of the posterior distribution.
This identification enables new and more efficient computational methods for
Bayesian inference with nonlinear forward models and Gaussian priors. In
particular, we approximate the posterior distribution as the product of a
lower-dimensional posterior defined on the LIS and the prior distribution
marginalized onto the complementary subspace. Markov chain Monte Carlo sampling
can then proceed in lower dimensions, with significant gains in computational
efficiency. We also introduce a Rao-Blackwellization strategy that
de-randomizes Monte Carlo estimates of posterior expectations for additional
variance reduction. We demonstrate the efficiency of our methods using two
numerical examples: inference of permeability in a groundwater system governed
by an elliptic PDE, and an atmospheric remote sensing problem based on Global
Ozone Monitoring System (GOMOS) observations
Physiological modeling of isoprene dynamics in exhaled breath
Human breath contains a myriad of endogenous volatile organic compounds
(VOCs) which are reflective of ongoing metabolic or physiological processes.
While research into the diagnostic potential and general medical relevance of
these trace gases is conducted on a considerable scale, little focus has been
given so far to a sound analysis of the quantitative relationships between
breath levels and the underlying systemic concentrations. This paper is devoted
to a thorough modeling study of the end-tidal breath dynamics associated with
isoprene, which serves as a paradigmatic example for the class of low-soluble,
blood-borne VOCs.
Real-time measurements of exhaled breath under an ergometer challenge reveal
characteristic changes of isoprene output in response to variations in
ventilation and perfusion. Here, a valid compartmental description of these
profiles is developed. By comparison with experimental data it is inferred that
the major part of breath isoprene variability during exercise conditions can be
attributed to an increased fractional perfusion of potential storage and
production sites, leading to higher levels of mixed venous blood concentrations
at the onset of physical activity. In this context, various lines of supportive
evidence for an extrahepatic tissue source of isoprene are presented.
Our model is a first step towards new guidelines for the breath gas analysis
of isoprene and is expected to aid further investigations regarding the
exhalation, storage, transport and biotransformation processes associated with
this important compound.Comment: 14 page
Physiological modeling of isoprene dynamics in exhaled breath
Human breath contains a myriad of endogenous volatile organic compounds
(VOCs) which are reflective of ongoing metabolic or physiological processes.
While research into the diagnostic potential and general medical relevance of
these trace gases is conducted on a considerable scale, little focus has been
given so far to a sound analysis of the quantitative relationships between
breath levels and the underlying systemic concentrations. This paper is devoted
to a thorough modeling study of the end-tidal breath dynamics associated with
isoprene, which serves as a paradigmatic example for the class of low-soluble,
blood-borne VOCs.
Real-time measurements of exhaled breath under an ergometer challenge reveal
characteristic changes of isoprene output in response to variations in
ventilation and perfusion. Here, a valid compartmental description of these
profiles is developed. By comparison with experimental data it is inferred that
the major part of breath isoprene variability during exercise conditions can be
attributed to an increased fractional perfusion of potential storage and
production sites, leading to higher levels of mixed venous blood concentrations
at the onset of physical activity. In this context, various lines of supportive
evidence for an extrahepatic tissue source of isoprene are presented.
Our model is a first step towards new guidelines for the breath gas analysis
of isoprene and is expected to aid further investigations regarding the
exhalation, storage, transport and biotransformation processes associated with
this important compound.Comment: 14 page
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