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13 results on '"School of Mathematics [Birmingham]"'

1. Solving Lasserre relaxations of unconstrained binary quadratic optimization problems by an interior-point method

Author

Habibi, Soodeh, Kočvara, Michal, Stingl, Michael, School of Mathematics [Birmingham], University of Birmingham [Birmingham], Department Mathematik [Erlangen], Friedrich-Alexander Universität Erlangen-Nürnberg (FAU), European Project: 813211,H2020-EU.1.3. - EXCELLENT SCIENCE - Marie Skłodowska-Curie Actions (Main Programme), and H2020-EU.1.3.1. - Fostering new skills by means of excellent initial training of researchers ,10.3030/813211,POEMA(2019)

Subjects
74P05, semidefinite optimization, interior-point methods, 65F08, MAXCUT problem MSC Classification: 90C22, 90C51, Binary quadratic optimization Lasserre hierarchy semidefinite optimization interior-point methods preconditioned conjugate gradients MAXCUT problem MSC Classification: 90C22 90C51 65F08 74P05, Binary quadratic optimization, [MATH]Mathematics [math], preconditioned conjugate gradients, Lasserre hierarchy
Abstract

The aim of this paper is to solve linear semidefinite programs arising from higher-order Lasserre relaxations of unconstrained binary quadratic optimization problems. For this we use an interior point method with a preconditioned conjugate gradient method solving the linear systems. The preconditioner utilizes the low-rank structure of the solution of the relaxations. In order to fully exploit this, we need to rewrite the moment relaxations. To treat the arising linear equality constraints we use an 1-penalty approach within the interior-point solver. The efficiency of this approach is demonstrated by numerical experiments with the MAXCUT and other randomly generated problems and a comparison with a state-of-the-art semidefinite solver and the ADMM method. As a by-product, we observe that the second-order relaxation is often high enough to deliver a globally optimal solution of the original problem.

Published
2023

2. Loraine - An interior-point solver for low-rank semidefinite programming

Author

Habibi, Soodeh, Kočvara, Michal, Stingl, Michael, School of Mathematics [Birmingham], University of Birmingham [Birmingham], Department Mathematik [Erlangen], Friedrich-Alexander Universität Erlangen-Nürnberg (FAU), European Project: 813211,H2020-EU.1.3. - EXCELLENT SCIENCE - Marie Skłodowska-Curie Actions (Main Programme), and H2020-EU.1.3.1. - Fostering new skills by means of excellent initial training of researchers ,10.3030/813211,POEMA(2019)

Subjects
truss topology optimization, 74P05, Semidefinite optimization interior-point methods preconditioned conjugate gradients truss topology optimization MAXCUT problem Lasserre relaxations sensor network localization AMS CLASSIFICATION 90C22 90C51 65F08 74P05, interior-point methods, 65F08, MAXCUT problem, 90C51, sensor network localization AMS CLASSIFICATION 90C22, [MATH]Mathematics [math], preconditioned conjugate gradients, Lasserre relaxations, Semidefinite optimization
Abstract

The aim of this paper is to introduce a new code for the solution of large-and-sparse linear Semidefinite Programs (SDPs) with low-rank solutions and/or low-rank data. We propose to use a preconditioned conjugate gradient method within an interior-point SDP algorithm and an efficient preconditioner fully utilizing the low-rank information. The efficiency is demonstrated by numerical experiments using the truss topology optimization problems, Lasserre relaxations of the MAXCUT problems and the sensor network localization problems.

Published
2023

3. Stochastic Primal Dual Hybrid Gradient Algorithm with Adaptive Step-Sizes

Author

Chambolle, Antonin, Delplancke, Claire, Ehrhardt, Matthias, Schönlieb, Carola-Bibiane, Tang, Junqi, CEntre de REcherches en MAthématiques de la DEcision (CEREMADE), Université Paris Dauphine-PSL, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS), Méthodes numériques pour le problème de Monge-Kantorovich et Applications en sciences sociales (MOKAPLAN), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Dauphine-PSL, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS)-Inria de Paris, Institut National de Recherche en Informatique et en Automatique (Inria)-Institut National de Recherche en Informatique et en Automatique (Inria), EDF R&D (EDF R&D), EDF (EDF), Department of Mathematical Sciences [Bath], University of Bath [Bath], Department of Applied Mathematics and Theoretical Physics [Cambridge] (DAMTP), Faculty of mathematics Centre for Mathematical Sciences [Cambridge] (CMS), University of Cambridge [UK] (CAM)-University of Cambridge [UK] (CAM), School of Mathematics [Birmingham], University of Birmingham [Birmingham], MJE acknowledges support from the EPSRC (EP/S026045/1, EP/T026693/1, EP/V026259/1) and the Leverhulme Trust (ECF-2019-478)., and CBS acknowledges support from the Philip Leverhulme Prize, the Royal Society Wolfson Fellowship, the EPSRC advanced career fellowship EP/V029428/1, EPSRC grants EP/S026045/1 and EP/T003553/1, EP/N014588/1, EP/T017961/1, the Wellcome Innovator Awards 215733/Z/19/Z and 221633/Z/20/Z, the European Union Horizon 2020 research and innovation programme under the Marie Skodowska-Curie grant agreement No. 777826 NoMADS, the Cantab Capital Institute for the Mathematics of Information and the Alan Turing Institute.

Subjects
47N10, 49J40, 65D18, 65K10, 90C06, 90C15, 90C25, 92C55, 94A08, Optimization and Control (math.OC), FOS: Mathematics, [MATH]Mathematics [math], Mathematics - Optimization and Control
Abstract

In this work we propose a new primal-dual algorithm with adaptive step-sizes. The stochastic primal-dual hybrid gradient (SPDHG) algorithm with constant step-sizes has become widely applied in large-scale convex optimization across many scientific fields due to its scalability. While the product of the primal and dual step-sizes is subject to an upper-bound in order to ensure convergence, the selection of the ratio of the step-sizes is critical in applications. Up-to-now there is no systematic and successful way of selecting the primal and dual step-sizes for SPDHG. In this work, we propose a general class of adaptive SPDHG (A-SPDHG) algorithms, and prove their convergence under weak assumptions. We also propose concrete parameters-updating strategies which satisfy the assumptions of our theory and thereby lead to convergent algorithms. Numerical examples on computed tomography demonstrate the effectiveness of the proposed schemes., 28 pages, 8 figures

Published
2023

4. Response to Letter to the Editor: 'Prevention of Adrenal Crisis: Cortisol Response to Major Stress Compared to Stress Dose Hydrocortisone Delivery'

Author

David J. Smith, Christopher J Mowatt, Angela E Taylor, Sibylle Kohler, Alessandro Prete, Radu Mihai, John Komninos, Niki Karavitaki, Dimitra Vassiliadi, Mark A. Foster, Violet Fazal-Sanderson, Brian G. Keevil, Joanne L. Fallowfield, Janet M. Lord, Donna M. O'Neil, Wiebke Arlt, Irina Bancos, John A.H. Wass, Djillali Annane, Merlan, Justine, University of Birmingham [Birmingham], Department of Internal Medicine, Division of Endocrinology, Diabetes, Metabolism, Nutrition, Mayo Clinic, School of Mathematics [Birmingham], Queens Elizabeth Hospital [Birmingham], Oxford Centre for Diabetes, Endocrinology and Metabolism (OCDEM), University of Oxford, Evangelismos Athens General Hospital, Royal Shrewsbury Hospital, Churchill Hospital Oxford Centre for Haematology, Hôpital Raymond Poincaré [AP-HP], Infection et inflammation (2I), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut National de la Santé et de la Recherche Médicale (INSERM), and University Hospital of South Manchester

Subjects
medicine.medical_specialty, Letter to the editor, Hydrocortisone, [SDV]Life Sciences [q-bio], Endocrinology, Diabetes and Metabolism, Clinical Biochemistry, Adrenocorticotropic hormone, Biochemistry, Endocrinology, Adrenocorticotropic Hormone, Internal medicine, Humans, Medicine, Online Only Articles, ComputingMilieux_MISCELLANEOUS, business.industry, Biochemistry (medical), Letters to the Editor Responses, Adrenal crisis, [SDV] Life Sciences [q-bio], Acute Disease, Cosyntropin, medicine.symptom, business, AcademicSubjects/MED00250, Adrenal Insufficiency, medicine.drug
Abstract

International audience

Published
2020
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5. The ON-TIME real-time railway traffic management framework: A proof-of-concept using a scalable standardised data communication architecture

Author

Joaquin Rodriguez, Bruno Ambrogio, Rob M.P. Goverde, Thomas Albrecht, Paola Pellegrini, Gemma Nicholson, Egidio Quaglietta, Twan Dollevoet, Grégory Marliere, Birgit Jaekel, Daniele Carcasole, Marco Giaroli, Delft University of Technology (TU Delft), Laboratoire Électronique Ondes et Signaux pour les Transports (IFSTTAR/COSYS/LEOST), Institut Français des Sciences et Technologies des Transports, de l'Aménagement et des Réseaux (IFSTTAR)-PRES Université Lille Nord de France, School of Mathematics and Statistics [Milton Keynes], Faculty of Science, Technology, Engineering and Mathematics [Milton Keynes], The Open University [Milton Keynes] (OU)-The Open University [Milton Keynes] (OU), Technische Universität Dresden = Dresden University of Technology (TU Dresden), Évaluation des Systèmes de Transports Automatisés et de leur Sécurité (IFSTTAR/COSYS/ESTAS), Erasmus University Medical Center [Rotterdam] (Erasmus MC), NTT Data, parent, Ansaldo energia (ITALIA), Ansaldo energia [Gênes], School of Mathematics [Birmingham], University of Birmingham [Birmingham], and Econometrics

Subjects
Engineering, Service (systems architecture), Distributed computing, Transport network, Interoperability, railML, Transportation, 010501 environmental sciences, TRAFFIC OPTIMISATION, 01 natural sciences, Transport engineering, ALGORITHME, Real-time Control System, 0502 economics and business, 0105 earth and related environmental sciences, Civil and Structural Engineering, RAILWAY TRAFFIC CONTROL, 050210 logistics & transportation, business.industry, OPTIMISATION, 05 social sciences, STANDARD COMMUNICATION ARCHITECTURE, Computer Science Applications, TRANSPORT FERROVIAIRE, TRAITEMENT EN TEMPS REEL, Automotive Engineering, Management system, Scalability, Systems architecture, REAL-TIME REPLANNING, [MATH.MATH-OC]Mathematics [math]/Optimization and Control [math.OC], REGULATION DU TRAFIC, business
Abstract

Automatic real-time control of traffic perturbations has recently become a central issue for many European railway infrastructure managers. The aim is to make use of mathematical algorithms to maintain the required service availability during unplanned disturbances to operations. In the literature many tools for real-time traffic control are proposed, but their effects on traffic have never been studied neither in real life nor in fully realistic simulation environments. We can mention only a few pilot tests and a unique installation in the Lötschberg Base tunnel in Switzerland, which uses a replanning framework that is generally applicable but does not consider a standard data communication format. Standardisation of railway data is instead one of the main requirements of the European Railway Traffic Management System (ERTMS) to enable traffic interoperability across different countries along the Trans-European Transport Network (TEN-T). Following this direction, this paper introduces one of the outputs of the European project ON-TIME: a framework for the automatic real-time management of railway traffic, designed for being standard and interoperable across different European railways. We make use of a web-based Service-Oriented Architecture to ensure scalability and flexibility of application. A standard railML interface is used for the input/output data of the modules, allowing immediate applicability of the framework to any network having a railML representation. A proof-of-concept is provided where the framework is tested in a closed-loop with the simulation environment HERMES for perturbed traffic scenarios on different networks in the UK, the Netherlands and Sweden. Tests are performed for two different replanning algorithms (ROMA and RECIFE) used for the automatic detection and optimised resolution of train conflicts. The two algorithms are compared on the test case in Sweden. Results show that the design of the proposed framework is effective in managing traffic perturbations and is extendible to real-life systems.Automatic real-time control of traffic perturbations has recently become a central issue for many European railway infrastructure managers. The aim is to make use of mathematical algorithms to maintain the required service availability during unplanned disturbances to operations. In the literature many tools for real-time traffic control are proposed, but their effects on traffic have never been studied neither in real life nor in fully realistic simulation environments. We can mention only a few pilot tests and a unique installation in the Lötschberg Base tunnel in Switzerland, which uses a replanning framework that is generally applicable but does not consider a standard data communication format. Standardisation of railway data is instead one of the main requirements of the European Railway Traffic Management System (ERTMS) to enable traffic interoperability across different countries along the Trans-European Transport Network (TEN-T). Following this direction, this paper introduces one of the outputs of the European project ON-TIME: a framework for the automatic real-time management of railway traffic, designed for being standard and interoperable across different European railways. We make use of a web-based Service-Oriented Architecture to ensure scalability and flexibility of application. A standard railML interface is used for the input/output data of the modules, allowing immediate applicability of the framework to any network having a railML representation. A proof-of-concept is provided where the framework is tested in a closed-loop with the simulation environment HERMES for perturbed traffic scenarios on different networks in the UK, the Netherlands and Sweden. Tests are performed for two different replanning algorithms (ROMA and RECIFE) used for the automatic detection and optimised resolution of train conflicts. The two algorithms are compared on the test case in Sweden. Results show that the design of the proposed framework is effective in managing traffic perturbations and is extendible to real-life systems.

Published
2016
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6. Information-theoretic thresholds from the cavity method

Author

Amin Coja-Oghlan, Will Perkins, Florent Krzakala, Lenka Zdeborová, Goethe-University Frankfurt am Main, Laboratoire de Physique Statistique de l'ENS (LPS), Fédération de recherche du Département de physique de l'Ecole Normale Supérieure - ENS Paris (FRDPENS), École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS)-École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), School of Mathematics [Birmingham], University of Birmingham [Birmingham], Institut de Physique Théorique - UMR CNRS 3681 (IPHT), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), European Project: 278857,EC:FP7:ERC,ERC-2011-StG_20101014,PTCC(2011), European Project: 307087,EC:FP7:ERC,ERC-2012-StG_20111012,SPARCS(2012), Université Paris Diderot - Paris 7 (UPD7)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Centre National de la Recherche Scientifique (CNRS)-Fédération de recherche du Département de physique de l'Ecole Normale Supérieure - ENS Paris (FRDPENS), Centre National de la Recherche Scientifique (CNRS)-École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS)-École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL), Centre National de la Recherche Scientifique (CNRS)-Université Paris-Saclay-Commissariat à l'énergie atomique et aux énergies alternatives (CEA), École normale supérieure - Paris (ENS Paris), and Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS)

Subjects
FOS: Computer and information sciences, Cavity method, Discrete Mathematics (cs.DM), General Mathematics, FOS: Physical sciences, 0102 computer and information sciences, 02 engineering and technology, [INFO.INFO-DM]Computer Science [cs]/Discrete Mathematics [cs.DM], Information theory, 01 natural sciences, Combinatorics, Stochastic block model, FOS: Mathematics, 0202 electrical engineering, electronic engineering, information engineering, Statistical inference, Constraint satisfaction problem, Mathematics, Random graph, Discrete mathematics, Conjecture, 68Q87, Probability (math.PR), 020206 networking & telecommunications, Probability and statistics, Mutual information, [MATH.MATH-PR]Mathematics [math]/Probability [math.PR], MSC classes: 68Q87, 010201 computation theory & mathematics, Physics - Data Analysis, Statistics and Probability, Generator matrix, Mathematics - Probability, Data Analysis, Statistics and Probability (physics.data-an), [PHYS.PHYS.PHYS-DATA-AN]Physics [physics]/Physics [physics]/Data Analysis, Statistics and Probability [physics.data-an], Computer Science - Discrete Mathematics
Abstract

Vindicating a sophisticated but non-rigorous physics approach called the cavity method, we establish a formula for the mutual information in statistical inference problems induced by random graphs and we show that the mutual information holds the key to understanding certain important phase transitions in random graph models. We work out several concrete applications of these general results. For instance, we pinpoint the exact condensation phase transition in the Potts antiferromagnet on the random graph, thereby improving prior approximate results [Contucci et al.: Communications in Mathematical Physics 2013]. Further, we prove the conjecture from [Krzakala et al.: PNAS 2007] about the condensation phase transition in the random graph coloring problem for any number $q\geq3$ of colors. Moreover, we prove the conjecture on the information-theoretic threshold in the disassortative stochastic block model [Decelle et al.: Phys. Rev. E 2011]. Additionally, our general result implies the conjectured formula for the mutual information in Low-Density Generator Matrix codes [Montanari: IEEE Transactions on Information Theory 2005].

Published
2017

7. Fine asymptotics of profiles and relaxation to equilibrium for growth-fragmentation equations with variable drift rates

Author

D. Balagué, José A. Cañizo, Pierre Gabriel, Departament de Matemàtiques [Barcelona] (UAB), Universitat Autònoma de Barcelona (UAB), School of Mathematics [Birmingham], University of Birmingham [Birmingham], Laboratoire de Mathématiques de Versailles (LMV), and Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)

Subjects
Physics, Numerical Analysis, exponential convergence, Exponential convergence, growth, 010102 general mathematics, Mathematical analysis, Eigenfunction, long-time behavior, 01 natural sciences, Power law, 010101 applied mathematics, Mathematics - Analysis of PDEs, Exponential growth, Fragmentation, Modeling and Simulation, FOS: Mathematics, eigenvalue problem, [MATH.MATH-AP]Mathematics [math]/Analysis of PDEs [math.AP], Entropy (information theory), Spectral gap, 0101 mathematics, entropy, Analysis of PDEs (math.AP)
Abstract

International audience; We are concerned with the long-time behavior of the growth-fragmentation equation. We prove fine estimates on the principal eigenfunctions of the growth-fragmentation operator, giving their first-order behavior close to $0$ and $+\infty$. Using these estimates we prove a spectral gap result by following the technique in [Caceres, Canizo, Mischler 2011, JMPA], which implies that solutions decay to the equilibrium exponentially fast. The growth and fragmentation coefficients we consider are quite general, essentially only assumed to behave asymptotically like power laws.

Published
2013
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8. The level set method for the two-sided max-plus eigenproblem

Author

Stéphane Gaubert, Sergei Sergeev, Centre de Mathématiques Appliquées - Ecole Polytechnique (CMAP), École polytechnique (X)-Centre National de la Recherche Scientifique (CNRS), Max-plus algebras and mathematics of decision (MAXPLUS), École polytechnique (X)-Centre National de la Recherche Scientifique (CNRS)-École polytechnique (X)-Centre National de la Recherche Scientifique (CNRS)-Inria Saclay - Ile de France, Institut National de Recherche en Informatique et en Automatique (Inria)-Institut National de Recherche en Informatique et en Automatique (Inria), School of Mathematics [Birmingham], and University of Birmingham [Birmingham]

Subjects
Level set (data structures), Level set method, [MATH.MATH-RA]Mathematics [math]/Rings and Algebras [math.RA], Spectrum (functional analysis), Function (mathematics), Lambda, Chebyshev distance, Combinatorics, Set (abstract data type), Matrix (mathematics), Control and Systems Engineering, Modeling and Simulation, [MATH.MATH-OC]Mathematics [math]/Optimization and Control [math.OC], Electrical and Electronic Engineering, [MATH.MATH-MG]Mathematics [math]/Metric Geometry [math.MG], Mathematics
Abstract

See also arXiv:1006.5702; International audience; We consider the max-plus analogue of the eigenproblem for matrix pencils Ax=lambda Bx. We show that the spectrum of (A,B) (i.e., the set of possible values of lambda), which is a finite union of intervals, can be computed in pseudo-polynomial number of operations, by a (pseudo-polynomial) number of calls to an oracle that computes the value of a mean payoff game. The proof relies on the introduction of a spectral function, which we interpret in terms of the least Chebyshev distance between Ax and lambda Bx. The spectrum is obtained as the zero level set of this function.

Published
2012
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9. Engineering and science highlights of the KAT-7 radio telescope

Author

W. New, D. Rosekrans, Nadeem Oozeer, F. Curtolo, M. Fijalkowski, S. Seranyane, A. Rust, J. R. Manley, I. P. Theron, N. Marais, A. C. Schröder, P. A. Woudt, R. T. Lord, Sharmila Goedhart, M. S. de Villiers, R. P. M. Julie, B. L. Fanaroff, Rob Fender, G. Coreejes, L. Sofeya, Claude Carignan, D. S. Shepherd, R. Lehmensiek, L. P. Williams, S. J. Marais, O. J. Mokone, Jonathan T. L. Zwart, R. Springbok, P. Gibbs, I. Liebenberg, P. Prozesky, Vanessa A. Moss, J. Horrell, Justin L. Jonas, R. van Rooyen, D. H. Botha, Roy Booth, A. Martens, L. G. Magnus, M. G. Welz, L. Richter, J. A. Malan, Tom Alberts, A. J. Tiplady, S. Mthembu, M. Madlavana, P. P. A. Kotzé, J. Grobbelaar, L. van den Heever, A. Langman, Venkatasubramani L. Thondikulam, S. Rajan, K. Cloete, S. Tshongweni, A. Peens-Hough, P. C. van Niekerk, N. J. Young, P. Herselman, S. J. Buchner, A. L. Walker, P. Macfarlane, F. Kapp, R. P. Armstrong, R. Spann, A. Dikgale, Kelley M. Hess, L. J. du Toit, M. Wolleben, M. Maree, J. Ludick, S. S. Passmoor, R. Siebrits, S. Blose, T. Cheetham, D. George, R. Renil, G. D. Nicholson, L. C. Schwardt, B. S. Frank, P. S. Swart, A. Loots, S. W. P. Esterhuyse, S. Wakhaba, C. J. T. van der Merwe, C. Magozore, T. W. Kusel, S. Ratcliffe, R. C. Crida, S. C. Gumede, M. Serylak, A. R. Foley, H. Bester, J. D. B. L. Jordaan, L. Marais, D. M. Lucero, S. D. Cross, D. Liebenberg, A. Barta, A. B. Pińska, E. F. Bauermeister, Dehann Fourie, O. Toruvanda, N. Hoek, Research School of Earth Sciences, Australian National University ( ANU ), Estrato Research and Development Ltd, Interdisciplinary Centre for Security, Reliability and Trust [Luxembourg] ( SnT ), Université du Luxembourg ( Uni.lu ), Faculty of Science, Technology and Communication [Luxembourg] ( FSTC ), University of Luxembourg [Luxembourg], Département de Physique [Montréal], Université de Montréal, Department of Paediatric Endocrinology, Royal Victoria Infirmary, Institute of Human Genetics, Centre for Life, Newcastle University [Newcastle], Développement et Communication Chimique chez les Insectes ( DCCI ), Centre National de la Recherche Scientifique ( CNRS ) -Université de Bourgogne ( UB ) -AgroSup Dijon - Institut National Supérieur des Sciences Agronomiques, de l'Alimentation et de l'Environnement, Animal Demography Unit, University of Cape Town, University of Southampton (Southampton, UK), Institute of Physics, University of Silesia, Rapita Systems Ltd [York], Department of Medical Oncology, Royal Melbourne Hospital, Brain and Mind Institute, Ecole Polytechnique Fédérale de Lausanne ( EPFL ), Service d'Explorations fonctionnelles multidisciplinaires [CHU Tenon], CHU Tenon [APHP]-Assistance publique - Hôpitaux de Paris - AP-HP (FRANCE), Service d'urologie [Mondor], Assistance publique - Hôpitaux de Paris (AP-HP)-Hôpital Henri Mondor-Université Paris-Est Créteil Val-de-Marne - Paris 12 ( UPEC UP12 ), OMedical Oncology, Guy's and St Thomas' Hospital [London], Institute of Cardiovascular and Medical Sciences, Electrocardiology Section, University of Glasgow, Glasgow, United Kingdom, Department of Computer and Information Science [Trondheim], Norwegian University of Science and Technology [Trondheim] ( NTNU ), Bordeaux Imaging Center ( BIC ), Université de Bordeaux ( UB ) -Institut François Magendie-Institut National de la Santé et de la Recherche Médicale ( INSERM ) -Centre National de la Recherche Scientifique ( CNRS ), Laboratoire de l'Accélérateur Linéaire ( LAL ), Université Paris-Sud - Paris 11 ( UP11 ) -Institut National de Physique Nucléaire et de Physique des Particules du CNRS ( IN2P3 ) -Centre National de la Recherche Scientifique ( CNRS ), School of Mathematics [Birmingham], University of Birmingham [Birmingham], Institut für Spezielle Botanik und Funktionelle Biodiversität, University of Leipzig, German Aerospace Center ( DLR ), University of the Western Cape, Unité Scientifique de la Station de Nançay ( USN ), Institut national des sciences de l'Univers ( INSU - CNRS ) -Observatoire de Paris-Université d'Orléans ( UO ) -Centre National de la Recherche Scientifique ( CNRS ), Materials Laboratory Rand Afrikaans University, Rand Afrikaans University, Jodrell Bank Centre for Astrophysics, University of Manchester [Manchester], School of Physics & DST-NRF, University of the Witwatersrand, University of the Witwatersrand [Johannesburg] ( WITS ), University of Southampton, Unité Scientifique de la Station de Nançay (USN), Centre National de la Recherche Scientifique (CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers en région Centre (OSUC), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO), Jodrell Bank Centre for Astrophysics (JBCA), University of the Witwatersrand [Johannesburg] (WITS), and Astronomy

Subjects
Cryogenic system, radio continuum: general, FOS: Physical sciences, 01 natural sciences, law.invention, Radio telescope, Telescope, Pulsar, law, 0103 physical sciences, Very-long-baseline interferometry, Aerospace engineering, Open architecture, instrumentation: interferometers, 010303 astronomy & astrophysics, Instrumentation and Methods for Astrophysics (astro-ph.IM), [ SDU.ASTR ] Sciences of the Universe [physics]/Astrophysics [astro-ph], Physics, Protocol data unit, 010308 nuclear & particles physics, business.industry, Astronomy, Astronomy and Astrophysics, [SDU.ASTR.IM]Sciences of the Universe [physics]/Astrophysics [astro-ph]/Instrumentation and Methods for Astrophysic [astro-ph.IM], Space and Planetary Science, business, Astrophysics - Instrumentation and Methods for Astrophysics, radio lines: general, [ SDU ] Sciences of the Universe [physics]
Abstract

The construction of the seven-dish Karoo Array Telescope (KAT-7) array in the Karoo region of the Northern Cape in South Africa was intended primarily as an engineering prototype for technologies and techniques applicable to the MeerKAT telescope. This paper looks at the main engineering and scientific highlights from this effort, and discusses their applicability to both MeerKAT and other next-generation radio telescopes. In particular, we found that the composite dish surface works well, but it becomes complicated to fabricate for a dish lacking circular symmetry; the Stirling cycle cryogenic system with ion pump to achieve vacuum works but demands much higher maintenance than an equivalent Gifford-McMahon cycle system; the ROACH (Reconfigurable Open Architecture Computing Hardware)-based correlator with SPEAD (Streaming Protocol for Exchanging Astronomical Data) protocol data transfer works very well and KATCP (Karoo Array Telescope Control Protocol) control protocol has proven very flexible and convenient. KAT-7 has also been used for scientific observations where it has a niche in mapping low surface-brightness continuum sources, some extended H I haloes and OH masers in star-forming regions. It can also be used to monitor continuum source variability, observe pulsars, and make Very Long Baseline Interferometry observations.

Published
2016
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10. A Geometrical Approach to Iterative Isotone Regression

Author

Nicolas Jégou, Arnaud Guyader, Sandor Nemeth, A. B. Németh, Applications of interacting particle systems to statistics ( ASPI ), Institut de Recherche Mathématique de Rennes ( IRMAR ), Université de Rennes 1 ( UR1 ), Université de Rennes ( UNIV-RENNES ) -Université de Rennes ( UNIV-RENNES ) -AGROCAMPUS OUEST-École normale supérieure - Rennes ( ENS Rennes ) -Institut National de Recherche en Informatique et en Automatique ( Inria ) -Institut National des Sciences Appliquées ( INSA ) -Université de Rennes 2 ( UR2 ), Université de Rennes ( UNIV-RENNES ) -Centre National de la Recherche Scientifique ( CNRS ) -Université de Rennes 1 ( UR1 ), Université de Rennes ( UNIV-RENNES ) -Centre National de la Recherche Scientifique ( CNRS ) -Inria Rennes – Bretagne Atlantique, Institut National de Recherche en Informatique et en Automatique ( Inria ), Université de Rennes ( UNIV-RENNES ) -Centre National de la Recherche Scientifique ( CNRS ), Centre de recherche en Statistique [Rennes], Université de Rennes 2 ( UR2 ), Université de Rennes ( UNIV-RENNES ) -Université de Rennes ( UNIV-RENNES ), Faculty of Mathematics and Computer Science [ Cluj-Napoca], Babeș-Bolyai University ( UBB ), School of Mathematics [Birmingham], University of Birmingham [Birmingham], Applications of interacting particle systems to statistics (ASPI), Institut de Recherche Mathématique de Rennes (IRMAR), AGROCAMPUS OUEST, Institut national d'enseignement supérieur pour l'agriculture, l'alimentation et l'environnement (Institut Agro)-Institut national d'enseignement supérieur pour l'agriculture, l'alimentation et l'environnement (Institut Agro)-Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Université de Rennes 2 (UR2), Université de Rennes (UNIV-RENNES)-École normale supérieure - Rennes (ENS Rennes)-Centre National de la Recherche Scientifique (CNRS)-Institut National des Sciences Appliquées - Rennes (INSA Rennes), Institut National des Sciences Appliquées (INSA)-Université de Rennes (UNIV-RENNES)-Institut National des Sciences Appliquées (INSA)-AGROCAMPUS OUEST, Institut National des Sciences Appliquées (INSA)-Université de Rennes (UNIV-RENNES)-Institut National des Sciences Appliquées (INSA)-Inria Rennes – Bretagne Atlantique, Institut National de Recherche en Informatique et en Automatique (Inria)-Institut National de Recherche en Informatique et en Automatique (Inria), Institut National des Sciences Appliquées (INSA)-Université de Rennes (UNIV-RENNES)-Institut National des Sciences Appliquées (INSA), Université de Rennes 2 (UR2), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES), Babes-Bolyai University [Cluj-Napoca] (UBB), Université de Rennes (UR)-Institut National des Sciences Appliquées - Rennes (INSA Rennes), Institut National des Sciences Appliquées (INSA)-Institut National des Sciences Appliquées (INSA)-École normale supérieure - Rennes (ENS Rennes)-Université de Rennes 2 (UR2)-Centre National de la Recherche Scientifique (CNRS)-INSTITUT AGRO Agrocampus Ouest, Institut national d'enseignement supérieur pour l'agriculture, l'alimentation et l'environnement (Institut Agro)-Institut national d'enseignement supérieur pour l'agriculture, l'alimentation et l'environnement (Institut Agro)-Université de Rennes (UR)-Institut National des Sciences Appliquées - Rennes (INSA Rennes), Institut national d'enseignement supérieur pour l'agriculture, l'alimentation et l'environnement (Institut Agro)-Institut national d'enseignement supérieur pour l'agriculture, l'alimentation et l'environnement (Institut Agro)-Inria Rennes – Bretagne Atlantique, Institut national d'enseignement supérieur pour l'agriculture, l'alimentation et l'environnement (Institut Agro)-Institut national d'enseignement supérieur pour l'agriculture, l'alimentation et l'environnement (Institut Agro), and ANR-11-LABX-0020,LEBESGUE,Centre de Mathématiques Henri Lebesgue : fondements, interactions, applications et Formation(2011)

Subjects
Statistics::Theory, Mathematical optimization, Iterative method, Applied Mathematics, Metric projection on convex cones, Nonparametric statistics, Univariate, Mathematics - Statistics Theory, Statistics Theory (math.ST), [STAT.TH]Statistics [stat]/Statistics Theory [stat.TH], [ STAT.TH ] Statistics [stat]/Statistics Theory [stat.TH], Projection (linear algebra), Computational Mathematics, 52A20, 62G08, 90C33, Bounded variation, FOS: Mathematics, Statistics::Methodology, Applied mathematics, Isotonic regression, Additive model, Nonparametric estimation, Additive models, Dykstra's projection algorithm, Mathematics
Abstract

In the present paper, we propose and analyze a novel method for estimating a univariate regression function of bounded variation. The underpinning idea is to combine two classical tools in nonparametric statistics, namely isotonic regression and the estimation of additive models. A geometrical interpretation enables us to link this iterative method with Von Neumann's algorithm. Moreover, making a connection with the general property of isotonicity of projection onto convex cones, we derive another equivalent algorithm and go further in the analysis. As iterating the algorithm leads to overfitting, several practical stopping criteria are also presented and discussed., Comment: 25 pages, 5 figures

Published
2014
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11. Generalizations of Bounds on the Index of Convergence to Weighted Digraphs

Author

Sergei Sergeev, Thomas Nowak, Hans Schneider, Glenn Merlet, Institut de Mathématiques de Marseille (I2M), Centre National de la Recherche Scientifique (CNRS)-École Centrale de Marseille (ECM)-Aix Marseille Université (AMU), Dynamics of Geometric Networks (DYOGENE), Département d'informatique - ENS Paris (DI-ENS), Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche en Informatique et en Automatique (Inria)-École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche en Informatique et en Automatique (Inria)-École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Inria Paris-Rocquencourt, Institut National de Recherche en Informatique et en Automatique (Inria), University of Wisconsin-Madison, School of Mathematics [Birmingham], University of Birmingham [Birmingham], IEEE Press, Aix Marseille Université (AMU)-École Centrale de Marseille (ECM)-Centre National de la Recherche Scientifique (CNRS), Département d'informatique de l'École normale supérieure (DI-ENS), École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut National de Recherche en Informatique et en Automatique (Inria)-Centre National de la Recherche Scientifique (CNRS)-École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut National de Recherche en Informatique et en Automatique (Inria)-Centre National de la Recherche Scientifique (CNRS)-Inria Paris-Rocquencourt, École normale supérieure - Paris (ENS-PSL), and Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut National de Recherche en Informatique et en Automatique (Inria)-Centre National de la Recherche Scientifique (CNRS)-École normale supérieure - Paris (ENS-PSL)

Subjects
Max algebra, Strongly connected component, Index (economics), [INFO.INFO-DM]Computer Science [cs]/Discrete Mathematics [cs.DM], Combinatorics, Index of convergence, Computer Science::Discrete Mathematics, Convergence (routing), FOS: Mathematics, Discrete Mathematics and Combinatorics, Mathematics - Combinatorics, 15A80, 15B48, 15A27, 15A21, Computer Science::Data Structures and Algorithms, Mathematics, Matrix powers, Mathematics::Combinatorics, Transient, Applied Mathematics, Digraph, weighted di-graphs, Directed graph, Nonnegative matrices, Optimal walks, Weighted digraphs, maximum walks, Combinatorics (math.CO)
Abstract

We study sequences of optimal walks of a growing length, in weighted digraphs, or equivalently, sequences of entries of max-algebraic matrix powers with growing exponents. It is known that these sequences are eventually periodic when the digraphs are strongly connected. The transient of such periodicity depends, in general, both on the size of digraph and on the magnitude of the weights. In this paper, we show that some bounds on the indices of periodicity of (unweighted) digraphs, such as the bounds of Wielandt, Dulmage-Mendelsohn, Schwarz, Kim and Gregory-Kirkland-Pullman, apply to the weights of optimal walks when one of their ends is a critical node., 17 pages, 3 figures

Published
2013
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12. Weak CSR expansions and transience bounds in max-plus algebra

Author

Merlet, Glenn, Nowak, Thomas, Sergeev, Sergeĭ, Institut de Mathématiques de Marseille (I2M), Centre National de la Recherche Scientifique (CNRS)-École Centrale de Marseille (ECM)-Aix Marseille Université (AMU), Dynamics of Geometric Networks (DYOGENE), Département d'informatique - ENS Paris (DI-ENS), Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche en Informatique et en Automatique (Inria)-École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche en Informatique et en Automatique (Inria)-École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Inria Paris-Rocquencourt, Institut National de Recherche en Informatique et en Automatique (Inria), School of Mathematics [Birmingham], University of Birmingham [Birmingham], Aix Marseille Université (AMU)-École Centrale de Marseille (ECM)-Centre National de la Recherche Scientifique (CNRS), Département d'informatique de l'École normale supérieure (DI-ENS), École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut National de Recherche en Informatique et en Automatique (Inria)-Centre National de la Recherche Scientifique (CNRS)-École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut National de Recherche en Informatique et en Automatique (Inria)-Centre National de la Recherche Scientifique (CNRS)-Inria Paris-Rocquencourt, École normale supérieure - Paris (ENS-PSL), and Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut National de Recherche en Informatique et en Automatique (Inria)-Centre National de la Recherche Scientifique (CNRS)-École normale supérieure - Paris (ENS-PSL)

Subjects
MSC 15A18, 15A23, 90B35, Numerical Analysis, Matrix powers, Periodicity, Algebra and Number Theory, Transient, 15A80, 15A23, 90B35, [INFO.INFO-DM]Computer Science [cs]/Discrete Mathematics [cs.DM], Max-plus, Digraphs, FOS: Mathematics, Discrete Mathematics and Combinatorics, Mathematics - Combinatorics, Geometry and Topology, Combinatorics (math.CO)
Abstract

This paper aims to unify and extend existing techniques for deriving upper bounds on the transient of max-plus matrix powers. To this aim, we introduce the concept of weak CSR expansions: A^t=CS^tR + B^t. We observe that most of the known bounds (implicitly) take the maximum of (i) a bound for the weak CSR expansion to hold, which does not depend on the values of the entries of the matrix but only on its pattern, and (ii) a bound for the CS^tR term to dominate. To improve and analyze (i), we consider various cycle replacement techniques and show that some of the known bounds for indices and exponents of digraphs apply here. We also show how to make use of various parameters of digraphs. To improve and analyze (ii), we introduce three different kinds of weak CSR expansions (named after Nachtigall, Hartman-Arguelles, and Cycle Threshold). As a result, we obtain a collection of bounds, in general incomparable to one another, but better than the bounds found in the literature., Comment: 32 pages

Published
2013
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13. Silver-doped bioactive glass fibres as a potential treatment for wound-associated bacterial biofilms.

Author

Shirgill S, Poologasundarampillai G, Jabbari S, Ward J, and Kuehne SA

Abstract

Chronic wounds are a drain on global health services and remain a major area of unmet clinical need. Chronic wounds are characterised by a stable and stubborn bacterial biofilm which hinders innate immune response and delays or prevents wound healing. Bioactive glass (BG) fibres offer a promising novel treatment for chronic wounds by targeting the wound-associated biofilm. In this study, the antimicrobial properties of silver-doped BG fibres were tested against Pseudomonas aeruginosa biofilms, which are commonly found in chronic wound infections. Results showed that BG fibres doped with silver resulted in a 5log10 reduction in biofilm formation whereas silver-free fibres only reduced formation by log10, therefore silver-doped fibres possess stronger antimicrobial effects. Moreover, there appeared to be a synergistic effect between the fibres and the silver as the application of the silver-doped fibres placed directly in contact with the forming biofilm resulted in a higher reduction in biofilm formation compared to treatments either: using the dissolution ions, using BG powder, or when the fibres were placed in an insert above the biofilm, inhibiting physical contact, instead. This suggests that the physical properties of the fibres, as well as silver, influence biofilm formation. Finally, results demonstrated that silver chloride, which is not antimicrobial, forms and the concentrations of antimicrobial silver species, namely silver ions and nanoparticles, reduce over time when fibres are soaked in cell culture media, which partially explains why the silver-doped dissolution ions contained lower antimicrobial activity compared to the fibres. As silver chloride is more likely to form with increased temperature and time, the antimicrobial activity of silver-containing dissolution ions is highly dependent on the length of ageing and storage conditions. Many studies investigate the antimicrobial and cytotoxic properties of biomaterials through their dissolution products. However, instability of antimicrobial silver species due to silver chloride formation and its effect on antimicrobial properties of silver-based biomaterials has not been reported before and could influence past and future dissolution-based assays as results showed that the antimicrobial activity of silver-based dissolution ions can vary greatly depending on post processing steps and can therefore produce misleading data., Competing Interests: The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:Sandeep Shirgill reports financial support was provided by 10.13039/501100000268Biotechnology and Biological Sciences Research Council. Gowsihan Poologasundarampillai reports financial support was provided by 10.13039/501100000266Engineering and Physical Sciences Research Council., (© 2023 The Authors.)

Published
2023
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