Search results for "Stability"

Asymptotic preserving IMEX finite volume schemes for low Mach number Euler equations with gravitation

2017

In this paper we will present and analyze a new class of the IMEX finite volume schemes for the Euler equations with a gravity source term. We will in particular concentrate on a singular limit of weakly compressible flows when the Mach number M1. In order to efficiently resolve slow dynamics we split the whole nonlinear system in a stiff linear part governing the acoustic and gravity waves and a non-stiff nonlinear part that models nonlinear advection effects. For time discretization we use a special class of the so-called globally stiffly accurate IMEX schemes and approximate the stiff linear operator implicitly and the non-stiff nonlinear operator explicitly. For spatial discretization t…

Combined impacts of the Allee effect, delay and stochasticity: Persistence analysis

2020

Abstract We study a combined influence of the Allee effect, delay and stochasticity on the base of the phenomenological Hassell mathematical model of population dynamics. This bistable dynamical model possesses a wide variety of regimes, both regular and chaotic. In the persistence zone, these regimes coexist with the trivial equilibrium that corresponds to the extinction of the population. It is shown that borders of the persistence zone are defined by the crisis and saddle-node bifurcation points. Noise-induced transitions from the persistence to the extinction are studied both numerically and analytically. Using numerical modeling, we have found that the persistence zone can decrease and…

Numerically stable computation of step-sizes for descent methods. The nonconvex case

1977

The computation of step-sizes which guarantee convergence in unconstrained minimization by descent methods is considered. The use of a “control” or “range” function is highly attractive for this purpose because of its simplicity. Since the Armijo-Goldstein test may fail prematurely due to numerical instability near the minimizer, we consider a range function based on gradient values alone as has been done forg convex in [8]. Numerical algorithms are given for the computation of step-sizes whose behaviour under roundoff is shown to be benign in the sense of F. L. Bauer [5].

Re-Clustering tool using an Open-Reference method that improves OTU definition

2019

International audience; 1.Environmental microbial communities are now widely studied using metabarcoding approaches, thanks to the democratization of high‐throughput DNA sequencing technologies. The massive number of reads produced with these technologies requires bioinformatic solutions to be treated. A key step in the analysis is to cluster reads into Operational Taxonomic Units (or OTUs) and thus reduce the amount of data for downstream analyses. Due to the important impact of the clustering method on the quantity and quality of OTUs, finding an equilibrium between the reliability and time‐consuming nature of the chosen strategy is a real challenge. The present article proposes a new pos…

SM identification of approximating models forH∞ robust control

1999

Set Membership (SM) W, identification of mixed parametric and nonparametric models is investigated, aimed to estimate a low order approximating model and an identification error, giving a measure of the unmodeled dynamics in a form well suited for H, control methodologies. In particular, the problem of estimating the parameters of the parametric part and the H, bound on the modeling error is solved using frequency domain data, supposing lbo bounded measurement errors and exponentially stable unmodeled dynamics. The effectiveness of the proposed procedure is tested on some numerical examples, showing the advantages of the proposed methods over the existing nonparametric H, identification app…

2020

This study examined the stability of reading difficulties (RD) from grades 2 to 6 and focused on the effects of measurement error and cut-off selection in the identification of RD and its stability with the use of simulations. It addressed methodological limitations of prior studies by (a) applying a model-based simulation analysis to examine the effects of measurement error and cut-offs in the identification of RD, (b) analyzing a non-English and larger sample, and (c) examining RD in both reading fluency and reading comprehension. Reading fluency and reading comprehension of 1,432 Finnish-speaking children were assessed in grades 2 and 6. In addition to the use of single cut-off points on…

Observer-based stabilization of spacecraft rendezvous with variable sampling and sensor nonlinearity

2013

Published version of an article in the journal: Mathematical Problems in Engineering. Also available from the publisher at: http://dx.doi.org/10.1155/2013/902452 Open Access This paper addresses the observer-based control problem of spacecraft rendezvous with nonuniform sampling period. The relative dynamic model is based on the classical Clohessy-Wiltshire equation, and sensor nonlinearity and sampling are considered together in a unified framework. The purpose of this paper is to perform an observer-based controller synthesis by using sampled and saturated output measurements, such that the resulting closed-loop system is exponentially stable. A time-dependent Lyapunov functional is devel…

State feedback control against sensor faults for Lipschitz nonlinear systems via new sliding mode observer techniques

2011

This paper investigates the problem of simultaneous state and fault estimation and observer-based fault tolerant controller design for Lipschitz nonlinear systems with sensor failure. A new estimation technique is presented in this paper to deal with this design problem. In the proposed approaches, the original system is first augmented by a descriptor model transformation, then a new Proportional and Derivative sliding mode observer technique is developed to obtain accurate estimations of both system states and sensor faults. The designing observer is generalized from the PD observer in [3], but is not a trivial extension. Based on the state estimates, a observer-based control strategy is …

Partition coefficient, blood to plasma ratio, protein binding and short-term stability of 11-nor-Delta(9)-carboxy tetrahydrocannabinol glucuronide.

2002

11-Nor-Delta(9)-carboxy tetrahydrocannabinol glucuronide (THCCOOglu) is a major metabolite of tetrahydrocannabinol in blood. Despite its mass spectrometric identification already in 1980, further physicochemical data of THCCOOglu have not been established. Therefore, the octanol/buffer partition coefficient P and the blood to plasma ratio b/p for THCCOOglu concentrations of 100 and 500ng/ml were investigated. Protein binding of the glucuronide was established from spiked albumin solutions at a level of 250ng/ml as well as from authentic samples. The data were compared to those of 11-nor-Delta(9)-carboxy tetrahydrocannabinol (THCCOOH). In addition, the short-term stability of THCCOOglu in pl…

Bridging vs. Chelating Coordination Modes of Vinylsilanes in CuIπ-Complexes: Structure and Stability

2013

Two new copper(I) olefin complexes, [Cu6Cl6(MTrVS)2] (1) and [Cu2Cl2(DMVSP)2] (2), of tridentate bridging methyltrivinylsilane (MTrVS) and bidentate chelating 2-[dimethyl(vinyl)silyl]pyridine (DMVSP) have been synthesized and characterized by single-crystal X-ray structure analysis, IR and 1H NMR spectroscopy. It has been shown that using the alkenylsilanes with required electronic properties, molecular symmetry and conformational flexibility, it is possible to control the formation of optimal copper(I) halide oligomers. The obtained results, together with relevant literature data, also illustrate how the coordination mode of vinylsilanes is related to Cu–(C=C) bond strengthening and, conse…