10 research outputs found
Defined Structural Features Can Favor Infective Endocarditis in Bovine Jugular Vein Valved Conduits
No full textDOI: 10.1007/s10915-006-9112-x Efficient Solution of Ax (k) = b (k) Using A −1
No full textwhere b (k+1) = f(x (k)). We show that when A is a full n × n matrix and K � cn, where c ≪ 1 depends on the specific software and hardware setup, it is faster to solve Ax (k) = b (k) for k = 1,...,K by explicitly evaluating the inverse matrix A −1 rather than through the LU decomposition of A. We also show that the forward error is comparable in both methods, regardless of the condition number of A. KEY WORDS: Matrix inversion; linear systems
Antiplatelet therapy abrogates platelet-assisted Staphylococcus aureus infectivity of biological heart valve conduits.
No full textAlthough recent advances in pulmonary valve replacement have enabled excellent hemodynamics, infective endocarditis remains a serious complication, particularly for implanted bovine jugular vein (BJV) conduits.
We investigated contributions by platelets and plasma fibrinogen to endocarditis initiation on various grafts used for valve replacement. Thus, adherence of Staphylococcus aureus and platelets to 5 graft tissues was studied quantitatively in perfusion chambers, assisted by microscopic analysis. We also evaluated standard antiplatelet therapy to prevent onset of S aureus endocarditis.
Of all tissues, bovine pericardium (BP) showed the greatest fibrinogen binding. Perfusion of all plasma-precoated tissues identified BP and BJV wall with the greatest affinity for S aureus. Perfusions of anticoagulated human blood over all tissues also triggered more platelet adhesion to BP and BJV wall as single platelets. Several controls confirmed that both S aureus and platelets were recruited on immobilized fibrinogen. In addition, perfusions (and controls) over plasma-coated tissues with whole blood, spiked with S aureus, revealed that bacteria exclusively bound to adhered platelets. Both the platelet adhesion and platelet-mediated S aureus recruitment required platelet α IIb β 3 and coated or soluble fibrinogen, respectively, interactions abrogated by the α IIb β 3 -antagonist eptifibatide. Also, standard antiplatelet therapy (aspirin/ticagrelor) reduced the adherence of S aureus in blood to BJV 3-fold.
Binding of plasma fibrinogen to especially BJV grafts enables adhesion of single platelets via α IIb β 3 . S aureus then attaches from blood to (activated) bound platelet α IIb β 3 via plasma fibrinogen. Dual antiplatelet therapy appears a realistic approach to prevent endocarditis and its associated mortality
Psi_B-energy operator and cross-power spectral density
No full textIn this paper we consider the hermitian extension of the cross-Psi_B-energy operator that we will denote by Psi_H. In addition, cross energy terms are formalized through multivariate signals representation. We investigate the connection between the interaction energy function of Psi_H and the cross-power spectral density (CPSD)of two complex valued signals. In particular, this link permits to use this operator for estimating the CPSD. We illustrate the interest of Psi_H as a similarity between a pair of signals in frequency domain on synthetic and real data
Why Do Some Grafts Used in Right Ventricular Outflow Tract Revalvulation Get Infected and Others Do Not?
No full textA New Approach to Synthesis of Questiomycin A: Oxidative Cyclocondensation of ortho‐Aminophenol.
No full textControlled NO-Release from 3D-Printed Small-Diameter Vascular Grafts Prevents Platelet Activation and Bacterial Infectivity
No full textThrombogenicity and bacterial infectiveness
are the most common
complications for foreign blood contacting surfaces associated with
functional failure of small-diameter vascular grafts (SDVGs). In this
work, novel bactericidal and nonthrombogenic SDVGs were manufactured
via 3D-printing technology, thus producing a controlled nitric oxide
(NO) release coating. S-Nitroso-N-acetyl-D-penicillamine (SNAP) was synthesized as an NO-donor, and
three biomedical grade composite matrixes of poly(ethylene glycol)
(PEG)-SNAP, polycaprolactone (PCL)-SNAP, and PEG-PCL-SNAP were validated
for water uptake and NO-release kinetics. To optimize and extend the
NO releasing profile, a PCL top-coat (tc) was deposited over the NO-releasing
layer. The PEG-PCL-SNAP-tc was selected for biological tests as its
NO-release profile was prolonged and well-controlled. Coating the
3D-printed SDVG with PEG-PCL-SNAP-tc resulted in quantitative antibacterial
features against both Gram-positive and Gram-negative bacteria and
in NO-mediated inhibition of platelet activation and aggregation.
Antibacterial and antithrombogenic properties in plasma are expected
to be as effective as in PBS, since NO release in plasma was not significantly
different from that in PBS. Overall, application of the inexpensive,
rapid, and reproducible 3D-printing technology as a custom-based production
method, in combination with a well-controlled NO release system, is
promising for the production of innovative bactericidal and hemocompatible
SDVGs
Infective endocarditis in patients after percutaneous pulmonary valve implantation with the stent-mounted bovine jugular vein valve : clinical experience and evaluation of the modified Duke criteria
No full textAIMS: Percutaneous pulmonary valve implantation (PPVI) has proven good hemodynamic results. As infective endocarditis (IE) remains a potential complication with limited available clinical data, we reviewed our patient records to improve future strategies of IE prevention, diagnosis and treatment. METHODS: Medical records of all patients diagnosed with Melody® valve IE according to the modified Duke criteria were retrospectively analyzed in three Belgian tertiary centers. RESULTS: 23 IE episodes in 22 out of 240 patients were identified (incidence 2.4% / patient year) with a clear male predominance (86%). Median age at IE was 17.9 years (range 8.2-45.9 years) and median time from PPVI to IE was 2.4 years (range 0.7-8 years). Streptococcal species caused 10 infections (43%), followed by Staphylococcus aureus (n = 5, 22%). In 13/23 IE episodes a possible entry-point was identified (57%). IE was classified as definite in 15 (65%) and as possible in 8 (35%) cases due to limitations of imaging. Echocardiography visualized vegetations in only 10 patients. PET-CT showed positive FDG signals in 5/7 patients (71%) and intracardiac echocardiography a vegetation in 1/1 patient (100%). Eleven cases (48%) had a hemodynamically relevant pulmonary stenosis at IE presentation. Nine early and 6 late percutaneous or surgical re-interventions were performed. No IE related deaths occurred. CONCLUSIONS: IE after Melody® valve PPVI is associated with a relevant need of re-interventions. Communication to patients and physicians about risk factors is essential in prevention. The modified Duke criteria underperformed in diagnosing definite IE, but inclusion of new imaging modalities might improve diagnostic performance.sponsorship: This work was supported by the Research Fund KU Leuven (OT/14/097). RH was sponsored by the Clinical Research Fund of UZ Leuven and the Flemish Research Foundation (FWO). (Research Fund KU Leuven|OT/14/097, Clinical Research Fund of UZ Leuven, Flemish Research Foundation (FWO))status: Publishe
Clinical Characteristics of Infective Endocarditis in Children
No full textBACKGROUND: Infective endocarditis (IE) remains a diagnostic and therapeutic challenge associated with high morbidity and mortality. We evaluated the microbial profile and clinical manifestation of IE in children. METHODS: A retrospective study examining pediatric IE cases treated between 2000 and 2017 at the Department of Pediatric Cardiology, KU Leuven, was conducted. Clinical presentation, treatment, complications, outcome of IE, underlying microorganisms and congenital heart defects were reviewed. RESULTS: Fifty-three patients were diagnosed with IE. Overall, 19 patients (36%) required cardiac surgery. Seven patients (13%) died. Eighty-seven percent of patients had an underlying congenital cardiac defect. Eighteen (34%) children presented with prosthetic graft IE. A causative organism was found in 49 (92%) cases: viridans group streptococci were identified in 17 (32%), Staphylococcus aureus in 13 (25%) and coagulase-negative staphylococci in 11 (20%) children. Community-acquired (CA) IE increased significantly from 8 (33%) cases in 2000-2007 to 20 (74%) cases in 2008-2017 (P < 0.01). Even with viridans streptococci being significantly more prevalent in the CA group (P < 0.01), we did not observe an increase of streptococcal IE from 2008 to 2017. Seventeen (32%) patients presented with hospital-acquired IE during the first year of life with 14 (82%) children after surgery and a prevalence of coagulase-negative staphylococci (53%). CONCLUSIONS: The incidence of pediatric IE was similar over the investigated time period with a shift toward CA IE. Streptococci and staphylococci accounted for the majority of cases in both periods. Awareness of IE and its prevention is crucial in patients after implantation of prosthetic grafts.sponsorship: This study was sponsored by a grant of the Research Fund KU Leuven (OT/14/097) given to R.H. T.R.V. was sponsored as a Postdoctoral Fellow of the Research Foundation Flanders (FWO Grant Number: 12K0916N) and R.H. by the Clinical Research Fund of UZ Leuven. (Research Fund KU Leuven|OT/14/097, Clinical Research Fund of UZ Leuven, Research Foundation Flanders (FWO)|12K0916N)status: Publishe
An Electromagnetic Analysis and Simulation of Scattering Problems and Diffractive Optical Elements
No full text本研究旨在利用時域頻譜配點補償法求解無限域中含複雜形狀散射體受電磁波入射所引致的散射現象，並且利用時域頻譜配點方法在設計與模擬繞射光學元件上。此法可用於分析材料含有不連續折射率分佈的電磁場問題，利用區域分割的概念，將整個計算域分割為數個子區域，尤其在不連續折射率處。每個子區域的場值先以Legendre多項式為基函數展開，在不同區域的邊界條件上利用特徵值傳輸。其中，補償項可以控制整個計算系統的穩定性與精確性。
於數值算例中，首先我們比較了幾個已有解析解的散射問題，例如：圓柱型的完美導體、圓柱型的介電材質、多層的圓柱型完美導體與介電材質，透過場等效原理所獲得的結果與解析解比對其準確性非常高。另外，我們也應用在較複雜的幾何形狀的散射體，也都得到良好的模擬結果。此外，我們利用時域頻譜配點方法模擬與設計繞射光學波導元件及繞射光學鏡片得到繞射光學元件的光學特性來驗證本方法的正確性與實用性。The purpose of this study is to solve scattering problems where
there is a complicated shape scatter interacting with incident
electromagnetic wave in an infinite spatial domain. The method can
be applied to analyze electromagnetic problems with material
containing discontinuous refractive indices. Employing the domain
decomposition, one can divide the whole computational domain into
several sub-domains, particularly at the interfaces of
discontinuous refractive indices. The electromagnetic fields in
each sub-domain can be expanded in terms of Legendre polynomial as
basis functions and at the boundary interface between different
regions, the characteristics are constructed and employed to
establish the penalty terms which are closely related to the
stability and flexibility of the method. Application to scattering
by a perfectly conducting and electric circular cylinder has been
carried out and compared with solution from field equivalent
principle. Extensions to more complicated geometries such as
perfectly electric square cylinder conductor and conducting with
dielectric layer where no analytical solution is available are
also simulated. Applications of the pseudospectral penalty method
to more practical optoelectronic devices such as diffractive optic
elements including diffractive optical waveguide and diffractive
optical lens are computed. All the present results are in good
agreement with available data in the literatures. With all the
results obtained, it can be concluded that the present
multi-domain pseudospectral penalty method in time domain provides
an alternative simulation method to the finite difference time
domain method for the electromagnetic wave propagation problems.
Although, the present work is restricted to two-dimensional
Maxwell equations, the extension to three-dimensional problems is
of no conceptual difficulty and will be the subject of future
work.Contents
1 Introduction 14
1.1 Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
1.2 Literature Review and Motivations . . . . . . . . . . . . . . . . . . . . 15
1.3 Content of The Thesis . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
2 Electromagnetics Preliminaries 19
2.1 Maxwell’s Equations . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
2.1.1 Differential Form of Maxwell’s Equations . . . . . . . . . . . . . 19
2.1.2 Constitutive Relations for Isotropic Medium . . . . . . . . . . . 20
2.2 Time-Harmonic Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
2.3 Boundary Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
2.4 Electromagnetic Potentials . . . . . . . . . . . . . . . . . . . . . . . . . 23
2.4.1 Magnetic Vector Potential ~A . . . . . . . . . . . . . . . . . . . 23
2.4.2 Electric Potential ~F . . . . . . . . . . . . . . . . . . . . . . . . . 25
2.5 Near to Far Field Transformation . . . . . . . . . . . . . . . . . . . . . 26
2.6 Radar Cross Section . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
3 Pseudospectral Penalty Methods for Time Domain Maxwell’s Equations
29
3.1 An Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
3.2 Pseudospectral Approximation Methods . . . . . . . . . . . . . . . . . 31
3.2.1 Legendre Pseudospectral Method . . . . . . . . . . . . . . . . . 31
3.2.2 Chebyshev Pseudospectral Method . . . . . . . . . . . . . . . . 33
3.3 Pseudospectral Penalty Method for Model PDE . . . . . . . . . . . . . 34
3.4 Pseudospectral Penalty Method and Two-Dimensional Maxwell’s Equations
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
3.4.1 Characteristic Variables and Well-posed Boundary Operator of
2-D Maxwell’s equations . . . . . . . . . . . . . . . . . . . . . . 36
3.4.2 Characteristic Representation of Physical Boundary Conditions 39
3.4.3 The Maxwell’s Equations with Pseudospectral Penalty Method 41
3.5 Absorbing Boundary Layers . . . . . . . . . . . . . . . . . . . . . . . . 43
3.6 Total Field and Scattered Field . . . . . . . . . . . . . . . . . . . . . . 44
3.7 Nearfield and Farfield Calculations . . . . . . . . . . . . . . . . . . . . 45
4 Two Dimensional Electromagnetic Wave Scattering Problems 49
4.1 Incident Plane Wave . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
4.1.1 Normal Incident Plane Wave : TEy Polarization . . . . . . . . . 49
4.1.2 Normal Incident Plane Wave : TMy Polarization . . . . . . . . 50
4.2 Scattering by Perfect Electric Conducting Medium . . . . . . . . . . . 50
4.2.1 Scattering by Circular Cylinder : TEy Polarization . . . . . . . 50
4.2.2 Scattering by Circular Cylinder : TMy Polarization . . . . . . . 53
4.2.3 Scattering by Square Cylinder : TEy Polarization . . . . . . . . 56
4.2.4 Scattering by Square Cylinder : TMy Polarization . . . . . . . . 57
4.3 Scattering by Dielectric Medium . . . . . . . . . . . . . . . . . . . . . 57
4.3.1 Scattering by Circular Cylinder : TEy Polarization . . . . . . . 57
4.3.2 Scattering by Circular Cylinder : TMy Polarization . . . . . . . 60
4.4 Scattering by Conducting and Dielectric Layered Objects . . . . . . . 64
4.4.1 Square Conductor with Layered Dielectric : TEy Polarization . 64
4.4.2 Square Conductor with Layered Dielectric : TMy Polarization . 65
5 Diffractive Optical Elements 121
5.1 Diffractive Optical Waveguide . . . . . . . . . . . . . . . . . . . . . . . 122
5.2 Diffractive Optical Lens . . . . . . . . . . . . . . . . . . . . . . . . . . 124
6 Conclusion 152
A Two Dimensional Full Space Green’s function 154
B Near to Far Field Field Transformation 15
