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Article ; Online: A Survey of Low-Rank Updates of Preconditioners for Sequences of Symmetric Linear Systems

Luca Bergamaschi

Algorithms, Vol 13, Iss 100, p

2020 Volume 100

Abstract: The aim of this survey is to review some recent developments in devising efficient preconditioners for sequences of symmetric positive definite (SPD) linear systems ... ... ... ... ... A ... ... k ... ... ... < ... ...

Abstract	The aim of this survey is to review some recent developments in devising efficient preconditioners for sequences of symmetric positive definite (SPD) linear systems <math display="inline"> <semantics> <mrow> <msub> <mi>A</mi> <mi>k</mi> </msub> <msub> <mi mathvariant="bold">x</mi> <mi>k</mi> </msub> <mo>=</mo> <msub> <mi mathvariant="bold">b</mi> <mi>k</mi> </msub> <mo>,</mo> <mi>k</mi> <mo>=</mo> <mn>1</mn> <mo>,</mo> <mi>…</mi> </mrow> </semantics> </math> arising in many scientific applications, such as discretization of transient Partial Differential Equations (PDEs), solution of eigenvalue problems, (Inexact) Newton methods applied to nonlinear systems, rational Krylov methods for computing a function of a matrix. In this paper, we will analyze a number of techniques of updating a given initial preconditioner by a low-rank matrix with the aim of improving the clustering of eigenvalues around 1, in order to speed-up the convergence of the Preconditioned Conjugate Gradient (PCG) method. We will also review some techniques to efficiently approximate the linearly independent vectors which constitute the low-rank corrections and whose choice is crucial for the effectiveness of the approach. Numerical results on real-life applications show that the performance of a given iterative solver can be very much enhanced by the use of low-rank updates.
Keywords	preconditioners ; conjugate gradient method ; sparse matrices ; low-rank updates ; Industrial engineering. Management engineering ; T55.4-60.8 ; Electronic computers. Computer science ; QA75.5-76.95
Subject code	518
Language	English
Publishing date	2020-04-01T00:00:00Z
Publisher	MDPI AG
Document type	Article ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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Article ; Online: Preventing Sudden Cardiac Death in Mitral Valve Prolapse

Anna Giulia Pavon / Luca Bergamaschi / Marco Guglielmo

Journal of Clinical Medicine, Vol 11, Iss 5112, p

When Multimodality Imaging Is the Key to Success

2022 Volume 5112

Abstract: Mitral valve prolapse (MVP) is a common cardiac anomaly that is estimated to affect 1–3% of the general population [.] ...

Abstract	Mitral valve prolapse (MVP) is a common cardiac anomaly that is estimated to affect 1–3% of the general population [.]
Keywords	n/a ; Medicine ; R
Language	English
Publishing date	2022-08-01T00:00:00Z
Publisher	MDPI AG
Document type	Article ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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Article ; Online: Scalable Block Preconditioners for Linearized Navier-Stokes Equations at High Reynolds Number

Filippo Zanetti / Luca Bergamaschi

Algorithms, Vol 13, Iss 199, p

2020 Volume 199

Abstract: We review a number of preconditioners for the advection-diffusion operator and for the Schur complement matrix, which, in turn, constitute the building blocks for Constraint and Triangular Preconditioners to accelerate the iterative solution of the ... ...

Abstract	We review a number of preconditioners for the advection-diffusion operator and for the Schur complement matrix, which, in turn, constitute the building blocks for Constraint and Triangular Preconditioners to accelerate the iterative solution of the discretized and linearized Navier-Stokes equations. An intensive numerical testing is performed onto the driven cavity problem with low values of the viscosity coefficient. We devise an efficient multigrid preconditioner for the advection-diffusion matrix, which, combined with the commuted BFBt Schur complement approximation, and inserted in a <math display="inline"><semantics><mrow><mn>2</mn><mo>×</mo><mn>2</mn></mrow></semantics></math> block preconditioner, provides convergence of the Generalized Minimal Residual (GMRES) method in a number of iteration independent of the meshsize for the lowest values of the viscosity parameter. The low-rank acceleration of such preconditioner is also investigated, showing its great potential.
Keywords	scalable preconditioners ; Navier-Stokes equations ; GMRES method ; low-rank updates ; multigrid ; Industrial engineering. Management engineering ; T55.4-60.8 ; Electronic computers. Computer science ; QA75.5-76.95
Subject code	532
Language	English
Publishing date	2020-08-01T00:00:00Z
Publisher	MDPI AG
Document type	Article ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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Article ; Online: The Non-Invasive Diagnosis of Chronic Coronary Syndrome

Léon Groenhoff / Giulia De Zan / Pietro Costantini / Agnese Siani / Eleonora Ostillio / Serena Carriero / Giuseppe Muscogiuri / Luca Bergamaschi / Giuseppe Patti / Carmine Pizzi / Sandro Sironi / Anna Giulia Pavon / Alessandro Carriero / Marco Guglielmo

Journal of Clinical Medicine, Vol 12, Iss 3793, p

A Focus on Stress Computed Tomography Perfusion and Stress Cardiac Magnetic Resonance

2023 Volume 3793

Abstract: Coronary artery disease is still a major cause of death and morbidity worldwide. In the setting of chronic coronary disease, demonstration of inducible ischemia is mandatory to address treatment. Consequently, scientific and technological efforts were ... ...

Abstract	Coronary artery disease is still a major cause of death and morbidity worldwide. In the setting of chronic coronary disease, demonstration of inducible ischemia is mandatory to address treatment. Consequently, scientific and technological efforts were made in response to the request for non-invasive diagnostic tools with better sensitivity and specificity. To date, clinicians have at their disposal a wide range of stress-imaging techniques. Among others, stress cardiac magnetic resonance (S-CMR) and computed tomography perfusion (CTP) techniques both demonstrated their diagnostic efficacy and prognostic value in clinical trials when compared to other non-invasive ischemia-assessing techniques and invasive fractional flow reserve measurement techniques. Standardized protocols for both S-CMR and CTP usually imply the administration of vasodilator agents to induce hyperemia and contrast agents to depict perfusion defects. However, both methods have their own limitations, meaning that optimizing their performance still requires a patient-tailored approach. This review focuses on the characteristics, drawbacks, and future perspectives of these two techniques.
Keywords	coronary artery disease ; cardiac coronary syndrome ; stress imaging ; cardiac computed tomography perfusion ; stress magnetic cardiac resonance ; Medicine ; R
Subject code	610
Language	English
Publishing date	2023-05-01T00:00:00Z
Publisher	MDPI AG
Document type	Article ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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Article ; Online: Block Preconditioning Matrices for the Newton Method to Compute the Dominant λ-Modes Associated with the Neutron Diffusion Equation

Amanda Carreño / Luca Bergamaschi / Angeles Martinez / Antoni Vidal-Ferrándiz / Damian Ginestar / Gumersindo Verdú

Mathematical and Computational Applications, Vol 24, Iss 1, p

2019 Volume 9

Abstract: In nuclear engineering, the λ -modes associated with the neutron diffusion equation are applied to study the criticality of reactors and to develop modal methods for the transient analysis. The differential eigenvalue problem that needs to be solved is ... ...

Abstract	In nuclear engineering, the λ -modes associated with the neutron diffusion equation are applied to study the criticality of reactors and to develop modal methods for the transient analysis. The differential eigenvalue problem that needs to be solved is discretized using a finite element method, obtaining a generalized algebraic eigenvalue problem whose associated matrices are large and sparse. Then, efficient methods are needed to solve this problem. In this work, we used a block generalized Newton method implemented with a matrix-free technique that does not store all matrices explicitly. This technique reduces mainly the computational memory and, in some cases, when the assembly of the matrices is an expensive task, the computational time. The main problem is that the block Newton method requires solving linear systems, which need to be preconditioned. The construction of preconditioners such as ILU or ICC based on a fully-assembled matrix is not efficient in terms of the memory with the matrix-free implementation. As an alternative, several block preconditioners are studied that only save a few block matrices in comparison with the full problem. To test the performance of these methodologies, different reactor problems are studied.
Keywords	block preconditioner ; generalized eigenvalue problem ; neutron diffusion equation ; modified block Newton method ; Applied mathematics. Quantitative methods ; T57-57.97 ; Mathematics ; QA1-939 ; Electronic computers. Computer science ; QA75.5-76.95
Subject code	518
Language	English
Publishing date	2019-01-01T00:00:00Z
Publisher	MDPI AG
Document type	Article ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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Article ; Online: Multimodality Imaging Evaluation to Detect Subtle Right Ventricular Involvement in Patients with Acute Myocarditis and Preserved Left Ventricular Ejection Fraction

Michela Bonanni / Gianmarco Angelini / Laura Anna Leo / Susanne Anna Schlossbauer / Luca Bergamaschi / Antonio Landi / Giuseppe Massimo Sangiorgi / Cinzia Forleo / Elena Pasotti / Giovanni Pedrazzini / Marco Valgimigli / Francesco F. Faletra / Marco Guglielmo / Anna Giulia Pavon

Journal of Clinical Medicine, Vol 12, Iss 4308, p

2023 Volume 4308

Abstract: Background: Evaluation of the right ventricle (RV) in patients with acute myocarditis (MY) remains challenging with both 2D transthoracic echocardiography (TTE) and cardiovascular magnetic resonance (CMR). We examined the incremental diagnostic value of ... ...

Abstract	Background: Evaluation of the right ventricle (RV) in patients with acute myocarditis (MY) remains challenging with both 2D transthoracic echocardiography (TTE) and cardiovascular magnetic resonance (CMR). We examined the incremental diagnostic value of CMR feature tracking (FT) to evaluate RV involvement in patients with myocarditis. Methods: We enrolled 54 patients with myocarditis and preserved left ventricle (LV) ejection fraction (EF). The CMR protocol included T2-weighted images for edema detection and late gadolinium enhancement (LGE) images. Global longitudinal strain (GLS) of the left ventricle (LV) and RV free wall strain (CMR-FWS) were obtained with CMR-FT. We identified 34 patients (62%) with inferior and lateral segment (IL-MY) involvement and 20 (38%) noIL-MY in case of any other myocardial segment involved. Here, 20 individuals who underwent CMR for suspected cardiac disease, which was not confirmed thereafter, were considered as the control population. Results: TTE and CMR showed normal RV function in all patients without visible RV involvement at the LGE or T2-weighted sequences. At CMR, LV-GLS values were significantly lower in patients with MY compared to the control group (median −19.0% vs. −21.0%, p = 0.029). Overall, CMR RV-FWS was no different between MY patients and controls (median −21.2% vs. −23.2 %, p = 0.201) while a significant difference was found between RV FWS in IL-MY and noIL-MY (median −18.17% vs. −24.2%, p = 0.004). Conclusions: CMR-FT has the potential to unravel subclinical RV involvement in patients with acute myocarditis, specifically in those with inferior and lateral injuries that exhibit lower RV-FWS values. In this setting, RV deformation analysis at CMR may be effectively implemented for a comprehensive functional assessment.
Keywords	cardiovascular magnetic resonance ; right ventricle ; acute myocarditis feature tracking CMR ; Medicine ; R
Subject code	610
Language	English
Publishing date	2023-06-01T00:00:00Z
Publisher	MDPI AG
Document type	Article ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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Article ; Online: Genetics and clinical phenotype of Erdheim–Chester disease

Lorenzo Bartoli / Francesco Angeli / Andrea Stefanizzi / Michele Fabrizio / Pasquale Paolisso / Luca Bergamaschi / Alessandro Broccoli / Pier Luigi Zinzani / Nazzareno Galiè / Paola Rucci / Alberto Foà / Carmine Pizzi

Frontiers in Cardiovascular Medicine, Vol

A case report of constrictive pericarditis and a systematic review of the literature

2022 Volume 9

Abstract: BackgroundErdheim–Chester disease (ECD) is a rare form of histiocytosis. An increasing number of genetic mutations have been associated with this syndrome, confirming its possible neoplastic origin. Recently, a connection between the BRAF mutational ... ...

Abstract	BackgroundErdheim–Chester disease (ECD) is a rare form of histiocytosis. An increasing number of genetic mutations have been associated with this syndrome, confirming its possible neoplastic origin. Recently, a connection between the BRAF mutational status and a specific phenotype was described; however, no studies have yet evaluated the correlations between other mutations and the clinical features of the disease.ObjectivesThis study aims to clarify the association between the clinical phenotype and genetic mutations identified in the neoplastic cell lines of ECD.MethodsWe describe a case of ECD characterized by pericardial involvement and a KRAS mutation shared with chronic myelomonocytic leukemia. Hence, through a meta-analysis of individual participant data of all genetically and clinically described cases of ECD in the literature, we aimed to elucidate the association between its clinical phenotype and baseline genetic mutations.ResultsOf the 760 studies screened, our review included 133 articles published from 2012 to April 2021. We identified 311 ECD patients whose genotype and phenotype were described. We found five main genes (BRAF, KRAS, NRAS, PIK3CA, and MAP2K1) whose mutation was reported at least three times. Mutation of BRAF led to a neurological disease (183 of 273 patients, 67%; p < 0.001); KRAS- and NRAS-mutated patients mainly showed cutaneous (five of six patients, 83.3%, p < 0.004) and pleural (four of nine patients, 44%, p = 0.002) involvement, respectively; PIK3CA was not associated with specific organ involvement; and MAP2K1 mutations caused the disease to primarily involve the peritoneum and retroperitoneum (4 of 11, 36.4%, p = 0.01).ConclusionThis work implies a possible influence of baseline mutation over the natural history of ECD, underscoring the importance of a thorough genetic analysis in all cases with the ultimate goal of identifying a possible targeted therapy for each patient.
Keywords	Erdheim-Chester disease ; constrictive pericarditis ; genotype ; phenotype ; precision medicine ; case-report ; Diseases of the circulatory (Cardiovascular) system ; RC666-701
Subject code	610
Language	English
Publishing date	2022-08-01T00:00:00Z
Publisher	Frontiers Media S.A.
Document type	Article ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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Article ; Online: Oral Surgery and Osteoradionecrosis in Patients Undergoing Head and Neck Radiation Therapy

Biomedicines, Vol 11, Iss 12, p

An Update of the Current Literature

2023 Volume 3339

Abstract: Osteoradionecrosis (ORN) is a serious long-term complication of head and neck radiotherapy (RT), which is often triggered by dental extractions. It results from avascular aseptic necrosis due to irradiated bone damage. ORN is challenging to treat and can ...

Abstract	Osteoradionecrosis (ORN) is a serious long-term complication of head and neck radiotherapy (RT), which is often triggered by dental extractions. It results from avascular aseptic necrosis due to irradiated bone damage. ORN is challenging to treat and can lead to severe complications. Furthermore, ORN causes pain and distress, significantly reducing the patient’s quality of life. There is currently no established preventive strategy. This narrative review aims to provide an update for the clinicians on the risk of ORN associated with oral surgery in head and neck RT patients, with a focus on the timing suitable for the oral surgery and possible ORN preventive treatments. An electronic search of articles was performed by consulting the PubMed database. Intervention and observational studies were included. A multidisciplinary approach to the patient is highly recommended to mitigate the risk of RT complications. A dental visit before commencing RT is highly advised to minimize the need for future dental extractions after irradiation, and thus the risk of ORN. Post-RT preventive strategies, in case of dento-alveolar surgery, have been proposed and include antibiotics, hyperbaric oxygen (HBO), and the combined use of pentoxifylline and tocopherol (“PENTO protocol”), but currently there is a lack of established standards of care. Some limitations in the use of HBO involve the low availability of HBO facilities, its high costs, and specific clinical contraindications; the PENTO protocol, on the other hand, although promising, lacks clinical trials to support its efficacy. Due to the enduring risk of ORN, removable prostheses are preferable to dental implants in these patients, as there is no consensus on the appropriate timing for their safe placement. Overall, established standards of care and high-quality evidence are lacking concerning both preventive strategies for ORN as well as the timing of the dental surgery. There is an urgent need to improve research for more efficacious clinical decision making.
Keywords	head and neck radiotherapy ; head and neck cancer ; osteoradionecrosis ; oral surgery ; oral medicine ; IMRT ; Biology (General) ; QH301-705.5
Subject code	610
Language	English
Publishing date	2023-12-01T00:00:00Z
Publisher	MDPI AG
Document type	Article ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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Article ; Online: Preliminary Experience With Low Molecular Weight Heparin Strategy in COVID-19 Patients

Pasquale Paolisso / Luca Bergamaschi / Emanuela Concetta D’Angelo / Francesco Donati / Maddalena Giannella / Sara Tedeschi / Renato Pascale / Michele Bartoletti / Giulia Tesini / Mauro Biffi / Benilde Cosmi / Carmine Pizzi / Pierluigi Viale / Nazzareno Galié

Frontiers in Pharmacology, Vol

2020 Volume 11

Abstract: BackgroundHeparin administration in COVID-19 patients is recommended by expert consensus, although evidence about dosage, duration and efficacy are limited. We aim to investigate the association between different dosages of low molecular weight heparin ( ... ...

Abstract	BackgroundHeparin administration in COVID-19 patients is recommended by expert consensus, although evidence about dosage, duration and efficacy are limited. We aim to investigate the association between different dosages of low molecular weight heparin (LMWH) and mortality among COVID-19 hospitalized patients.Methods and ResultsRetrospective study of 450 laboratory-confirmed COVID-19 patients admitted to Sant’Orsola Bologna Hospital from March 01 to April 10, 2020. Clinical, laboratory and treatment data were collected and analyzed. The in-hospital mortality between COVID-19 patients treated with standard prophylactic LMWH dosage vs. intermediate LMWH dosage was compared. Out of 450 patients, 361 received standard deep vein thrombosis (DVT) prophylaxis enoxaparin treatment (40-60mg daily) and 89 patients received intermediate enoxaparin dosage (40–60 mg twice daily) for 7 days. No significant differences in the main demographic characteristics and laboratory testings at admission were observed in the two heparin regimen subgroups, except for older age and prevalence of hypertension in the group treated with “standard” prophylaxis LMWH dosage. The intermediate LMWH administration was associated with a lower in-hospital all-cause mortality compared to the “standard” prophylactic LMWH dosage (18.8% vs. 5.8%, p = 0.02). This difference remained significant after adjustment with the propensity score for variables that differed significantly between the dosage groups (OR= 0.260, 95% CI 0.089–0.758, p=0.014).ConclusionsIntermediate LMWH dosage seems to be associated with lower incidence of mortality compared to standard DVT prophylaxys in hospitalized COVID-19 patients. Our study paves the way to further pathophysiological investigations and controlled studies of anticoagulation therapy in Covid-19 disease.
Keywords	COVID- 19 ; heparin ; LMWH (low molecular weight heparin) ; in-hospital mortality ; DVT prophylaxis ; Therapeutics. Pharmacology ; RM1-950 ; covid19
Subject code	610
Language	English
Publishing date	2020-08-01T00:00:00Z
Publisher	Frontiers Media S.A.
Document type	Article ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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Article ; Online: Gli uccelli della provincia di Novara (Piemonte, Italia)

Fabio Casale / Ettore Rigamonti / Marco Ricci / Luca Bergamaschi / Raffaele Cennamo / Angelo Garanzini / Leonardo Mostini / Alessandro Re / Valentina Toninelli / Mauro Fasola

Rivista Italiana di Ornitologia - Research in Ornithology, Vol 87, Iss

distribuzione, abbondanza e stato di conservazione

2017 Volume 1

Abstract: In questo lavoro viene riportato un elenco commentato degli uccelli noti per la provincia di Novara (1.340 km2) aggiornato al 31/12/2016 e vengono forniti dati di sintesi relativi alle attività di monitoraggio condotte in anni recenti (2009-2016). I dati ...

Abstract	In questo lavoro viene riportato un elenco commentato degli uccelli noti per la provincia di Novara (1.340 km2) aggiornato al 31/12/2016 e vengono forniti dati di sintesi relativi alle attività di monitoraggio condotte in anni recenti (2009-2016). I dati sono stati raccolti sia attraverso revisione bibliografica sia attraverso attività di ricerca diretta sul campo. L’avifauna della provincia di Novara annovera o ha annoverato (dal 1860 al 2016) 304 specie delle quali 135 nidificanti certe o probabili in tempi recenti (dopo il 2000), 85 di interesse comunitario (Allegato I della Direttiva “Uccelli”), 116 SPEC - Species of European Conservation Concern secondo BirdLife International e 53 inserite nella European Red List of Birds. L’area è di importanza europea e/o nazionale per la nidificazione di specie di interesse conservazionistico quali Egretta garzetta (650-1.100 nidi), Nycticorax nycticorax (200-300 nidi), Botaurus stellaris (5-7 maschi cantori), Ciconia nigra (1-2 coppie), Ciconia ciconia (4-6 coppie), Himantopus himantopus (300-500 coppie), Vanellus vanellus (500-600 coppie), Columba oenas (20-30 coppie), nonché per la migrazione di Philomachus pugnax (5.000-7.000 ind.) e Tringa glareola (500-1.500 ind.). Negli ultimi anni (2009-2016) si segnalano in particolare: la nidificazione accertata per la prima volta nel Novarese di Ardea alba, Galerida cristata e Lullula arborea; il ritorno di Burhinus oedicnemus e Chlidonias niger in periodo riproduttivo dopo decenni di assenza; la colonizzazione da parte di Dryocopus martius degli ambienti forestali di collina e di pianura.
Keywords	Provincia di Novara ; risaie ; garzaie ; migrazione ; Garzetta ; Nitticora ; Zoology ; QL1-991
Language	English
Publishing date	2017-05-01T00:00:00Z
Publisher	PAGEPress Publications
Document type	Article ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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