10 research outputs found
Model Reduction for Aperiodically Sampled Data Systems
Two approaches to moment matching based model reduction of aperiodically
sampled data systems are given. The term "aperiodic sampling" is used in the
paper to indicate that the time between two consecutive sampling instants can
take its value from a pre-specified finite set of allowed sampling intervals.
Such systems can be represented by discrete-time linear switched (LS) state
space (SS) models. One of the approaches investigated in the paper is to apply
model reduction by moment matching on the linear time-invariant (LTI) plant
model, then compare the responses of the LS SS models acquired from the
original and reduced order LTI plants. The second approach is to apply a moment
matching based model reduction method on the LS SS model acquired from the
original LTI plant, and then compare the responses of the original and reduced
LS SS models. It is proven that for both methods, as long as the original LTI
plant is stable, the resulting reduced order LS SS model of the sampled data
system is quadratically stable. The results from two approaches are compared
with numerical examples
Model Reduction by Moment Matching for Linear Switched Systems
Two moment-matching methods for model reduction of linear switched systems
(LSSs) are presented. The methods are similar to the Krylov subspace methods
used for moment matching for linear systems. The more general one of the two
methods, is based on the so called "nice selection" of some vectors in the
reachability or observability space of the LSS. The underlying theory is
closely related to the (partial) realization theory of LSSs. In this paper, the
connection of the methods to the realization theory of LSSs is provided, and
algorithms are developed for the purpose of model reduction. Conditions for
applicability of the methods for model reduction are stated and finally the
results are illustrated on numerical examples.Comment: Sent for publication in IEEE TAC, on October 201
Model Reduction of Linear Switched Systems by Restricting Discrete Dynamics
We present a procedure for reducing the number of continuous states of
discrete-time linear switched systems, such that the reduced system has the
same behavior as the original system for a subset of switching sequences. The
proposed method is expected to be useful for abstraction based control
synthesis methods for hybrid systems
Moment Matching Based Model Reduction for LPV State-Space Models
We present a novel algorithm for reducing the state dimension, i.e. order, of
linear parameter varying (LPV) discrete-time state-space (SS) models with
affine dependence on the scheduling variable. The input-output behavior of the
reduced order model approximates that of the original model. In fact, for input
and scheduling sequences of a certain length, the input-output behaviors of the
reduced and original model coincide. The proposed method can also be
interpreted as a reachability and observability reduction (minimization)
procedure for LPV-SS representations with affine dependence
Reachability and Observability Reduction for Linear Switched Systems with Constrained Switching
International audienceWe present an algorithm for reducing the number of continuous states of a discrete time linear switched system, such that the reduced system has the same input–output behavior as the original system for a subset of switching sequences. The procedure can be interpreted as reachability and observability reduction for a linear switched system with constrained switching. The proposed method is expected to be useful for abstraction based control synthesis methods for hybrid systems
Model Reduction by Nice Selections for Linear Switched Systems
International audienc
Hyperfocusing as a dimension of adult attention deficit hyperactivity disorder
Patients with Attention Deficit Hyperactivity Disorder (ADHD) suffer not
only from inability to focus but also from inability to shift attention
for events that trigger their interests. This phenomenon is called
``hyperfocusing{''}. Previous literature about hyperfocusing is scarce
and relies mainly on case reports. The study aimed to investigate and
compare the severity of hyperfocusing in adult ADHD with and without
psycho-stimulant use. ADHD (DSM-IV-TR) patients either psycho-stimulant
naive (n = 53) or on psycho-stimulants (n = 79) from two ADHD clinics
were recruited. The control group (n = 65) consisted of healthy
university students. A socio-demographic form, the Beck Depression
Inventory, the Wender-Utah Rating Scale, the Adult ADHD Self- Report
Scale and the Hyperfocusing Scale were applied to the participants.
There was no difference between total Hyperfocusing Scale and Adult ADHD
Self-Report Scale scores of two patient groups, but both have higher
scores than controls (p < 0.001). Hyperfocusing is higher in adult ADHD
and there was no difference between stimulant-naive patients or patients
on stimulants. Hyperfocusing can be defined as a separate dimension of
adult ADHD. (C) 2016 Elsevier Ltd. All rights reserved
Tocilizumab treatment in severe COVID-19: a multicenter retrospective study with matched controls
Coronavirus disease-2019 (COVID-19) associated pneumonia may progress into acute respiratory distress syndrome (ARDS). Some patients develop features of macrophage activation syndrome (MAS). Elevated levels of IL-6 were reported to be associated with severe disease, and anti-IL-6R tocilizumab has been shown to be effective in some patients. This retrospective multicenter case-control study aimed to evaluate the efficacy of tocilizumab in hospitalized COVID-19 patients, who received standard of care with or without tocilizumab. Primary outcome was the progression to intubation or death. PSMATCH (SAS) procedure was used to achieve exact propensity score (PS) matching. Data from 1289 patients were collected, and study population was reduced to 1073 based on inclusion-exclusion criteria. The composite outcome was observed more frequently in tocilizumab-users, but there was a significant imbalance between arms in all critical parameters. Primary analyses were carried out in 348 patients (174 in each arm) after exact PS matching according to gender, ferritin, and procalcitonin. Logistic regression models revealed that tocilizumab significantly reduced the intubation or death (OR 0.40, p = 0.0017). When intubation is considered alone, tocilizumab-users had > 60% reduction in odds of intubation. Multiple imputation approach, which increased the size of the matched patients up to 506, provided no significant difference between arms despite a similar trend for intubation alone group. Analysis of this retrospective cohort showed more frequent intubation or death in tocilizumab-users, but PS-matched analyses revealed significant results for supporting tocilizumab use overall in a subset of patients matched according to gender, ferritin and procalcitonin levels