Search results for "Time optimal"
showing 10 items of 16 documents
Invitation to participate in a multi-center study for validation of cerebral computed tomography angiography and computed tomography perfusion in the…
2021
In recent years commensal microorganisms are not just “passive occupants”, but important element of homeostasis. There are numerous reports documenting the composition and role of the gut, skin or vagina microbiome but the role of commensal organisms living in the lungs is relatively unknown. Pulmonary microbiome impact on the immune response of the host organism and may indicate new therapeutic directions. Lung microbiome, by modulating the expression of innate immunity genes, causes an increase in the concentration of IL-5, IL-10, IFNγ and CCL11, affects the TLR4 dependent response of pulmonary macrophages and modulate the production of antibacterial peptides contained in the mucus. It is…
Vegetation Types Mapping Using Multi-Temporal Landsat Images in the Google Earth Engine Platform
2021
Vegetation Types (VTs) are important managerial units, and their identification serves as essential tools for the conservation of land covers. Despite a long history of Earth observation applications to assess and monitor land covers, the quantitative detection of sparse VTs remains problematic, especially in arid and semiarid areas. This research aimed to identify appropriate multi-temporal datasets to improve the accuracy of VTs classification in a heterogeneous landscape in Central Zagros, Iran. To do so, first the Normalized Difference Vegetation Index (NDVI) temporal profile of each VT was identified in the study area for the period of 2018, 2019, and 2020. This data revealed strong se…
Time optimal control of a satellite with two rotors
2001
International audience; The aim of this work is to investigate the structure of time-optimal trajectories for a control system modelizing a satellite with two rotors attached along its two fixed axes. Our results extend to the general case those obtained by Sussmann and Tang in an unpublished paper where they treat a particular case described below. We end up finding a sufficient family of four parameters trajectory types. The main tools used are the Pontryagin Maximum Principle, switching functions and envelope theory. © 2001 EUCA.
An oxygen monitoring and control system inside a malaxation machine to improve extra virgin olive oil quality
2013
In recent years, oxygen content regulation during malaxation has been noted as a process parameter. The aim of this study was to identify the optimal time during the malaxation process of the olives of the Sicilian cultivar Nocellara del Belice when the presence of oxygen in the machine headspace activates the enzyme complex in favour of the volatile compounds, without compromising the phenolic composition. During the malaxation process, the atmosphere inside the malaxation machine was modified by blowing pure oxygen from cylinders at specific stages of the process (i.e., 5, 15, 25, and 35 min after the start of malaxation), using a system that allows the automatic and continuous maintenanc…
Non-readmission decisions in the intensive care unit under French rules: A nationwide survey of practices.
2018
International audience; Purpose: We investigated, using a multicentre survey of practices in France, the practices of ICU physicians concerning the decision not to readmit to the ICU, in light of current legislation.Materials and methods: Multicentre survey of practices among French ICU physicians via electronic questionnaire in January 2016. Questions related to respondents’ practices regarding re-admission of patients to the ICU and how these decisions were made. Criteria were evaluated by the health care professionals as regards importance for non-readmission.Results: In total, 167 physicians agreed to participate, of whom 165 (99%) actually returned a completed questionnaire from 58 ICU…
The generic local structure of time-optimal synthesis with a target of codimension one in dimension greater than two
1997
In previous papers, we gave in dimension 2 and 3 a classification of generic synthesis of analytic systems\(\dot v(t) = X(v(t)) + u(t)Y(v(t))\) with a terminal submanifoldN of codimension one when the trajectories are not tangent toN. We complete here this classification in all generic cases in dimension 3, giving a topological classification and a model in each case. We prove also that in dimensionn≥3, out of a subvariety ofN of codimension there, we have described all the local synthesis.
Towards the time-optimal control of dissipative spin-1/2 particles in nuclear magnetic resonance
2011
International audience; We consider the time-optimal control of a spin 1/2 particle whose dynamics is governed by the Bloch equations with both longitudinal and transverse relaxation terms. We solve this control problem by using geometric optimal control techniques. We show the crucial role of singular extremals in the time-optimal synthesis. This role can mainly be attributed to the presence of dissipation. We also analyze the robustness of the optimal control sequence when both the maximum amplitude of the control field and the dissipative parameters are varied. Finally, we present an experimental implementation of the different solutions using techniques of Nuclear Magnetic Resonance.
Time-optimal selective pulses of two uncoupled spin-1/2 particles
2018
We investigate the time-optimal solution of the selective control of two uncoupled spin 1/2 particles. Using the Pontryagin Maximum Principle, we derive the global time-optimal pulses for two spins with different offsets. We show that the Pontryagin Hamiltonian can be written as a one-dimensional effective Hamiltonian. The optimal fields can be expressed analytically in terms of elliptic integrals. The time-optimal control problem is solved for the selective inversion and excitation processes. A bifurcation in the structure of the control fields occurs for a specific offset threshold. In particular, we show that for small offsets, the optimal solution is the concatenation of regular and sin…
Time-optimal control of SU(2) quantum operations
2013
We propose an analysis of the time-optimal control of SU(2) quantum operations. By using the Pontryagin Maximum Principle, we show how to determine the optimal trajectory reaching a given target state. Explicit analytical solutions are given for two specific examples. We discuss the role of the detuning in the construction of the optimal synthesis.
Time-optimal control of the purification of a qubit in contact with a structured environment
2019
We investigate the time-optimal control of the purification of a qubit interacting with a structured environment, consisting of a strongly coupled two-level defect in interaction with a thermal bath. On the basis of a geometric analysis, we show for weak and strong interaction strengths that the optimal control strategy corresponds to a qubit in resonance with the reservoir mode. We investigate under which conditions qubit coherence and correlation between the qubit and the environment can speed up the control process.