Search

Your search keyword '"Ionescu, A. C."' showing total 714 results
Start Over Author "Ionescu, A. C."
714 results on '"Ionescu, A. C."'

1. Moment matching based reduced closed-loop design to achieve asymptotic performance

Author

Ionescu, Tudor C.

Subjects
Mathematics - Optimization and Control, Mathematics - Dynamical Systems
Abstract

In this paper, the moment matching techniques are adopted to obtain reduced-order closed-loop systems with reduced-order controllers that maintain the closed-loop stability and guarantee desired asymptotic performance, after revealing the relationship between the Internal Model Principle used in control design and the time-domain moment matching problem. As a result, the design of a low order controller can be done starting from considering the achieving of asymptotic performance as a moment matching problem, resulting in a reduced order closed-loop system., Comment: 7 pages. Preliminary resukts have been presented in CDC2013

Published
2024

3. Time-Domain Moment Matching for Second-Order Systems

Author

Cheng, Xiaodong, Ionescu, Tudor C., and Pătraşcu, Monica

Subjects
Mathematics - Optimization and Control
Abstract

This paper studies a structure-preserving model reduction problem for large-scale second-order dynamical systems via the framework of time-domain moment matching. The moments of a second-order system are interpreted as the solutions of second-order Sylvester equations, which leads to families of parameterized second-order reduced models that match the moments of an original second-order system at selected interpolation points. Based on this, a two-sided moment matching problem is addressed, providing a unique second-order reduced system that match two distinct sets interpolation points. Furthermore, we also construct the reduced second-order systems that matches the moments of both zero and first order derivative of the original second-order system. Finally, the Loewner framework is extended to the second-order systems, where two parameterized families of models are presented that retain the second-order structure and interpolate sets of tangential data.

Published
2023

5. Model reduction with pole-zero placement and high order moment matching

Author

Ionescu, Tudor C., Iftime, Orest V., and Necoara, Ion

Subjects
Mathematics - Optimization and Control
Abstract

In this paper, we compute a low order approximation of a system of large order $n$ that matches $\nu$ moments of order $j_i$ of the transfer function, at $\nu$ interpolation points, has $\ell$ poles and $k$ zeros fixed and also matches $\nu-(\ell +k)$ moments of order $j_i+1$, where $j_i+1$ is the multiplicity of the $i$-th interpolation point. We derive explicit linear systems in the free parameters to simultaneously achieve the required pole-zero placement and match the desired high order moments. We compute the closed form of the free parameters that meet the constraints, as the solution of a $\nu$ order linear system. Furthermore, for data-driven model reduction, we generalize the construction of the Loewner matrices to include the data and the imposed pole and higher order moment constraints. The resulting approximations achieve a trade-off between the good norm approximation and the preservation of the dynamics of the original system in a region of interest., Comment: 7 pages

Published
2020

6. A population-scale temporal case–control evaluation of COVID-19 disease phenotype and related outcome rates in patients with cancer in England (UKCCP)

Author

Starkey, Thomas, Ionescu, Maria C., Tilby, Michael, Little, Martin, Burke, Emma, Fittall, Matthew W., Khan, Sam, Liu, Justin K. H., Platt, James R., Mew, Rosie, Tripathy, Arvind R., Watts, Isabella, Williams, Sophie Therese, Appanna, Nathan, Al-Hajji, Youssra, Barnard, Matthew, Benny, Liza, Burnett, Alexander, Bytyci, Jola, Cattell, Emma L., Cheng, Vinton, Clark, James J., Eastlake, Leonie, Gerrand, Kate, Ghafoor, Qamar, Grumett, Simon, Harper-Wynne, Catherine, Kahn, Rachel, Lee, Alvin J. X., Lomas, Oliver, Lydon, Anna, Mckenzie, Hayley, Panneerselvam, Hari, Pascoe, Jennifer S., Patel, Grisma, Patel, Vijay, Potter, Vanessa A., Randle, Amelia, Rigg, Anne S., Robinson, Tim M., Roylance, Rebecca, Roques, Tom W., Rozmanowski, Stefan, Roux, René L., Shah, Ketan, Sheehan, Remarez, Sintler, Martin, Swarup, Sanskriti, Taylor, Harriet, Tillett, Tania, Tuthill, Mark, Williams, Sarah, Ying, Yuxin, Beggs, Andrew, Iveson, Tim, Lee, Siow Ming, Middleton, Gary, Middleton, Mark, Protheroe, Andrew, Fowler, Tom, Johnson, Peter, and Lee, Lennard Y. W.

Published
2023
Full Text
View/download PDF

9. H2 model reduction of linear network systems by moment matching and optimization

Author

Necoara, I. and Ionescu, T. C.

Subjects
Mathematics - Optimization and Control
Abstract

In this paper we study the problem of model reduction of linear network systems. We aim at computing a reduced order stable approximation of the network with the same topology and optimal w.r.t. H2 norm error approximation. Our approach is based on time-domain moment matching framework, where we optimize over families of parameterized reduced order models matching a set of moments at arbitrary interpolation points. The parameterization of the low order models is in terms of the free parameters and of the interpolation points. For this family of parameterized models we formulate an optimization-based model reduction problem with the H2 norm of error approximation as objective function while the preservation of some structural and physical properties yields the constraints. This problem is nonconvex and we write it in terms of the Gramians of a minimal realization of the error system. We propose two solutions for this problem. The first solution assumes that the error system admits a block diagonal observability Gramian, allowing for a simple convex reformulation as semidefinite programming, but at the cost of some performance loss. We also derive sufficient conditions to guarantee block diagonalization of the Gramian. The second solution employs a gradient projection method for a smooth reformulation yielding (locally) optimal interpolation points and free parameters. The potential of the methods is illustrated on a power network., Comment: 11 pages

Published
2019

10. Optimal H2 moment matching-based model reduction for linear systems by (non)convex optimization

Author

Necoara, I. and Ionescu, T. C.

Subjects
Mathematics - Optimization and Control, 93A30, 93C05, 90C26
Abstract

In this paper we compute families of reduced order models that match a prescribed set of moments of a highly dimensional linear time-invariant system. First, we fully parametrize the models in the interpolation points and in the free parameters, and then we fix the set of interpolation points and parametrize the models only in the free parameters. Based on these two parametrizations and using as objective function the H2-norm of the error approximation we derive non-convex optimization problems, i.e., we search for the optimal free parameters and even the interpolation points to determine the approximation model yielding the minimal H2-norm error. Further, we provide the necessary first-order optimality conditions for these optimization problems given explicitly in terms of the controllability and the observability Gramians of a minimal realization of the error system. Using the optimality conditions, we propose gradient type methods for solving the corresponding optimization problems, with mathematical guarantees on their convergence. We also derive convex SDP relaxations for these problems and analyze when the convex relaxations are exact. We illustrate numerically the efficiency of our results on several test examples., Comment: 25 pages

Published
2018

12. COVID-19: Third dose booster vaccine effectiveness against breakthrough coronavirus infection, hospitalisations and death in patients with cancer: A population-based study

Author

Kinloch, Emma, Lam, Emily, Murphy, Gillian, Rhodes, Malcolm, Robinson, Kate, Swarup, Sanskriti, Bernhardt, Keeley, Bytyci, Jola, Ying, Yuxin, Johal, Sukhmunni, Sheehan, Remarez, Lee, Lennard Y.W., Ionescu, Maria C., Starkey, Thomas, Little, Martin, Tilby, Michael, Tripathy, Arvind R., Mckenzie, Hayley S., Al-Hajji, Youssra, Appanna, Nathan, Barnard, Matthew, Benny, Liza, Burnett, Alexander, Cattell, Emma L., Clark, James J., Khan, Sam, Ghafoor, Qamar, Panneerselvam, Hari, Illsley, George, Harper-Wynne, Catherine, Hattersley, Rosie J., Lee, Alvin JX., Lomas, Oliver, Liu, Justin KH., McCauley, Amanda, Pang, Matthew, Pascoe, Jennifer S., Platt, James R., Patel, Grisma, Patel, Vijay, Potter, Vanessa A., Randle, Amelia, Rigg, Anne S., Robinson, Tim M., Roques, Tom W., Roux, René L., Rozmanowski, Stefan, Taylor, Harriet, Tuthill, Mark H., Watts, Isabella, Williams, Sarah, Beggs, Andrew, Iveson, Tim, Lee, Siow M., Middleton, Gary, Middleton, Mark, Protheroe, Andrew, Fittall, Matthew W., Fowler, Tom, and Johnson, Peter

Published
2022
Full Text
View/download PDF

15. Vaccine effectiveness against COVID-19 breakthrough infections in patients with cancer (UKCCEP): a population-based test-negative case-control study

Author

Kinloch, Emma, Lam, Emily, Murphy, Gillian, Rhodes, Malcolm, Robinson, Kate, Lee, Lennard Y W, Starkey, Thomas, Ionescu, Maria C, Little, Martin, Tilby, Michael, Tripathy, Arvind R, Mckenzie, Hayley S, Al-Hajji, Youssra, Barnard, Matthew, Benny, Liza, Burnett, Alexander, Cattell, Emma L, Charman, Jackie, Clark, James J, Khan, Sam, Ghafoor, Qamar, Illsley, George, Harper-Wynne, Catherine, Hattersley, Rosie J, Lee, Alvin J X, Leonard, Pauline C, Liu, Justin K H, Pang, Matthew, Pascoe, Jennifer S, Platt, James R, Potter, Vanessa A, Randle, Amelia, Rigg, Anne S, Robinson, Tim M, Roques, Tom W, Roux, René L, Rozmanowski, Stefan, Tuthill, Mark H, Watts, Isabella, Williams, Sarah, Iveson, Tim, Lee, Siow Ming, Middleton, Gary, Middleton, Mark, Protheroe, Andrew, Fittall, Matthew W, Fowler, Tom, and Johnson, Peter

Published
2022
Full Text
View/download PDF

21. Romania's Holy War: Soldiers, Motivation, and the Holocaust. Grant T Harward.

Author

Ionescu, Stefan C

Subjects
MILITARY crimes, CRIMES against prisoners, MASS murder, WORLD War II, WAR
Abstract

"Romania's Holy War: Soldiers, Motivation, and the Holocaust" by Grant T. Harward explores the role of Romanian soldiers in the mass killing of Jews, Roma, and other civilians during World War II. The book delves into the soldiers' motivations, which included nationalism, anti-communism, religion, and antisemitism. Harward's study sheds light on the Romanian army's participation in atrocities against civilians and expands the theoretical understanding of military crimes. The book provides a critical examination of a neglected chapter in Romania's history and aims to spark a national discussion on the soldiers' actions and motivations during the Holocaust. [Extracted from the article]

Published
2024
Full Text
View/download PDF

22. Families of moment matching based, structure preserving approximations for linear port Hamiltonian systems

Author

Ionescu, Tudor C. and Astolfi, Alessandro

Subjects
Mathematics - Dynamical Systems
Abstract

In this paper we propose a solution to the problem of moment matching with preservation of the port Hamiltonian structure, in the framework of time-domain moment matching. We characterize several families of parameterized port Hamiltonian models that match the moments of a given port Hamiltonian system, at a set of finite interpolation points. We also discuss the problem of Markov parameters matching for linear systems as a moment matching problem for descriptor representations associated to the given system, at zero interpolation points. Solving this problem yields families of parameterized reduced order models that achieve Markov parameter matching. Finally, we apply these results to the port Hamiltonian case, resulting in families of parameterized reduced order port Hamiltonian approximations., Comment: 27 pages, 8 figures, Automatica journal

Published
2013
Full Text
View/download PDF

31. Cellulose Nanocrystals Show Anti-Adherent and Anti-Biofilm Properties against Oral Microorganisms.

Author

Panio, Antonella, Ionescu, Andrei C., La Ferla, Barbara, Zoia, Luca, Savadori, Paolo, Tartaglia, Gianluca M., and Brambilla, Eugenio

Subjects
*CELLULOSE nanocrystals, *ORAL microbiology, *STREPTOCOCCUS mutans, *CANDIDA albicans, *CIRCULAR economy, *AQUEOUS solutions
Abstract

Cellulose nanocrystals (CNCs) are cellulose-derived nanomaterials that can be easily obtained, e.g., from vegetable waste produced by circular economies. They show promising antimicrobial activity and an absence of side effects and toxicity. This study investigated the ability of CNCs to reduce microbial adherence and biofilm formation using in vitro microbiological models reproducing the oral environment. Microbial adherence by microbial strains of oral interest, Streptococcus mutans and Candida albicans, was evaluated on the surfaces of salivary pellicle-coated enamel disks in the presence of different aqueous solutions of CNCs. The anti-biofilm activity of the same CNC solutions was tested against S. mutans and an oral microcosm model based on mixed plaque inoculum using a continuous-flow bioreactor. Results showed the excellent anti-adherent activity of the CNCs against the tested strains from the lowest concentration tested (0.032 wt. %, p < 0.001). Such activity was significantly higher against S. mutans than against C. albicans (p < 0.01), suggesting a selective anti-adherent activity against pathogenic strains. At the same time, there was a minimal, albeit significant, anti-biofilm activity (0.5 and 4 wt. % CNC solution for S. mutans and oral microcosm, respectively, p = 0.01). This makes CNCs particularly interesting as anticaries agents, encouraging their use in the oral field. [ABSTRACT FROM AUTHOR]

Published
2024
Full Text
View/download PDF

32. In Vitro Characterization of Hydroxyapatite-Based Coatings Doped with Mg or Zn Electrochemically Deposited on Nanostructured Titanium.

Author

Vranceanu, Diana M., Ungureanu, Elena, Ionescu, Ionut C., Parau, Anca C., Pruna, Vasile, Titorencu, Irina, Badea, Mihaela, Gălbău, Cristina-Ștefania, Idomir, Mihaela, Dinu, Mihaela, Alina Vladescu, and Cotrut, Cosmin M.

Subjects
SURFACE coatings, CONTACT angle, TITANIUM, TITANIUM dioxide, FREE surfaces, ZINC alloys, HYDROXYAPATITE
Abstract

Biomaterials are an important and integrated part of modern medicine, and their development and improvement are essential. The fundamental requirement of a biomaterial is found to be in its interaction with the surrounding environment, with which it must coexist. The aim of this study was to assess the biological characteristics of hydroxyapatite (HAp)-based coatings doped with Mg and Zn ions obtained by the pulsed galvanostatic electrochemical method on the surface of pure titanium (cp-Ti) functionalized with titanium dioxide nanotubes (NTs TiO2) obtained by anodic oxidation. The obtained results highlighted that the addition of Zn or Mg into the HAp structure enhances the in vitro response of the cp-Ti surface functionalized with NT TiO2. The contact angle and surface free energy showed that all the developed surfaces have a hydrophilic character in comparison with the cp-Ti surface. The HAp-based coatings doped with Zn registered superior values than the ones with Mg, in terms of biomineralization, electrochemical behavior, and cell interaction. Overall, it can be said that the addition of Mg or Zn can enhance the in vitro behavior of the HAp-based coatings in accordance with clinical requirements. Antibacterial tests showed that the proposed HAp-Mg coatings had no efficiency against Escherichia coli, while the HAp-Zn coatings registered the highest antibacterial efficiency. [ABSTRACT FROM AUTHOR]

Published
2024
Full Text
View/download PDF

33. Pain distress: the negative emotion associated with procedures in ICU patients

Author

Puntillo, Kathleen A., Max, Adeline, Timsit, Jean-Francois, Ruckly, Stephane, Chanques, Gerald, Robleda, Gemma, Roche-Campo, Ferran, Mancebo, Jordi, Divatia, Jigeeshu V., Soares, Marcio, Ionescu, Daniela C., Grintescu, Ioana M., Maggiore, Salvatore Maurizio, Rusinova, Katerina, Owczuk, Radoslaw, Egerod, Ingrid, Papathanassoglou, Elizabeth D. E., Kyranou, Maria, Joynt, Gavin M., Burghi, Gaston, Freebairn, Ross C., Ho, Kwok M., Kaarlola, Anne, Gerritsen, Rik T., Kesecioglu, Jozef, Sulaj, Miroslav M. S., Norrenberg, Michelle, Benoit, Dominique D., Seha, Myriam S. G., Hennein, Akram, Pereira, Fernando J., Benbenishty, Julie S., Abroug, Fekri, Aquilina, Andrew, Monte, Julia R. C., An, Youzhong, and Azoulay, Elie

Published
2018
Full Text
View/download PDF

38. Abstract 804: The temporal evolution in disease phenotype of COVID-19 hospitalisation, intensive care and case fatality rates in cancer patients across the United Kingdom (UKCCP)

Author

Starkey, Thomas, primary, Ionescu, Maria C., additional, Fittall, Matthew W., additional, Tilby, Michael, additional, Burnett, Alex, additional, Hattersley, Rosie, additional, Khan, Sam, additional, Little, Martin, additional, Liu, Justin K., additional, Platt, James R., additional, Tripathy, Arvind, additional, Watts, Isabella, additional, Williams, Sophie Therese, additional, Programme, United Kingdom COVID Cancer, additional, Fowler, Tom, additional, Johnson, Peter W., additional, and Lee, Lennard Y., additional

Published
2023
Full Text
View/download PDF

46. Nonlinear Cross Gramians

Author

Ionescu, Tudor C., Scherpen, Jacquelien M. A., Korytowski, Adam, editor, Malanowski, Kazimierz, editor, Mitkowski, Wojciech, editor, and Szymkat, Maciej, editor

Published
2009
Full Text
View/download PDF

49. Positive Real Balancing for Nonlinear Systems

Author

Ionescu, Tudor C., Scherpen, Jacquelien M. A., Bock, Hans-Georg, editor, de Hoog, Frank, editor, Friedman, Avner, editor, Gupta, Arvind, editor, Neunzert, Helmut, editor, Pulleyblank, William R., editor, Rusten, Torgeir, editor, Santosa, Fadil, editor, Tornberg, Anna-Karin, editor, Ciuprina, Gabriela, editor, and Ioan, Daniel, editor

Published
2007
Full Text
View/download PDF

Catalog

Books, media, physical & digital resources
See catalog results