224 research outputs found
Vortex ring refraction at large Froude numbers
We have experimentally studied the impact of an initially planar axisymmetric
vortex ring, incident at an oblique angle, upon a gravity-induced interface
separating two fluids of differing densities. After impact, the vortex ring was
found to exhibit a variety of subsequent trajectories, which we organize
according to both the incidence angle, , and the interface strength,
defined as the ratio of the Atwood and Froude numbers, . For grazing
incidence angles ( deg.) vortices either penetrate or
reflect from the interface, depending on whether the interface is weak or
strong. In some cases, reflected vortices execute damped oscillations before
finally disintegrating. For smaller incidence angles (
deg.) vortices penetrate the interface. When there is a strong interface, these
vortices are observed to curve back up toward the interface. When there is a
weak interface, these vortices are observed to refract downward, away from the
interface. The critical interface strength below which vortex ring refraction
is observed is given by .Comment: 26 pages, 11 figures; Submitted to Physical Review
Infrared spectroscopy of diatomic molecules - a fractional calculus approach
The eigenvalue spectrum of the fractional quantum harmonic oscillator is
calculated numerically solving the fractional Schr\"odinger equation based on
the Riemann and Caputo definition of a fractional derivative. The fractional
approach allows a smooth transition between vibrational and rotational type
spectra, which is shown to be an appropriate tool to analyze IR spectra of
diatomic molecules.Comment: revised + extended version, 9 pages, 6 figure
Early cost-utility analysis of tissue-engineered heart valves compared to bioprostheses in the aortic position in elderly patients
__Objectives:__ Aortic valve disease is the most frequent indication for heart valve replacement with the highest prevalence in elderly. Tissue-engineered heart valves (TEHV) are foreseen to have important advantages over currently used bioprosthetic heart valve substitutes, most importantly reducing valve degeneration with subsequent reduction of re-intervention. We performed early Health Technology Assessment of hypothetical TEHV in elderly patients (â„ 70Â years) requiring surgical (SAVR) or transcatheter aortic valve implantation (TAVI) to assess the potential of TEHV and to inform future development decisions.
__Methods:__ Using a patient-level simulation model, the potential cost-effectiveness of TEHV compared with bioprostheses was predicted from a societal perspective. Anticipated, but currently hypothetical improvements in performance of TEHV, divided in durability, thrombogenicity, and infection resistance, were explored in scenario analyses to estimate quality-adjusted life-year (QALY) gain, cost reduction, headroom, and budget impact.
__Results:__ Durability of TEHV had the highest impact on QALY gain and costs, followed by infection resistance. Improved TEHV performance (â 50% prosthetic valve-related events) resulted in lifetime QALY gains of 0.131 and 0.043, lifetime cost reductions of âŹ639 and âŹ368, translating to headrooms of âŹ3255 and âŹ2498 per hypothetical TEHV compared to SAVR and TAVI, respectively. National savings in the first decade after implementation varied between âŹ2.8 and âŹ11.2 million (SAVR) and âŹ3.2ââŹ12.8 million (TAVI) for TEHV substitution rates of 25â100%.
__Conclusions:__ Despite the relatively short life expectancy of elderly patients undergoing SAVR/TAVI, hypothetical TEHV are predicted to be cost-effective compared to bioprostheses, commercially viable and result in national cost savings when biomedical engineers succeed in realising improved durability and/or infection resistance of TEHV
Ten Misconceptions from the History of Analysis and Their Debunking
The widespread idea that infinitesimals were "eliminated" by the "great
triumvirate" of Cantor, Dedekind, and Weierstrass is refuted by an
uninterrupted chain of work on infinitesimal-enriched number systems. The
elimination claim is an oversimplification created by triumvirate followers,
who tend to view the history of analysis as a pre-ordained march toward the
radiant future of Weierstrassian epsilontics. In the present text, we document
distortions of the history of analysis stemming from the triumvirate ideology
of ontological minimalism, which identified the continuum with a single number
system. Such anachronistic distortions characterize the received interpretation
of Stevin, Leibniz, d'Alembert, Cauchy, and others.Comment: 46 pages, 4 figures; Foundations of Science (2012). arXiv admin note:
text overlap with arXiv:1108.2885 and arXiv:1110.545
What is the potential of tissue-engineered pulmonary valves in children?
BACKGROUND: As a living heart valve substitute with growth potential and improved durability, tissue-engineered heart valves (TEHV) may prevent re-interventions that are currently often needed in children with congenital heart disease. We performed early Health Technology Assessment to assess the potential cost-effectiveness of TEHV in children requiring right ventricular outflow tract reconstruction (RVOTR).
METHODS: A systematic review and meta-analysis was conducted of studies reporting clinical outcome after RVOTR with existing heart valve substitutes in children published between 1/1/2000-2/5/2018. Using a patient-level simulation model, costs and effects of RVOTR with TEHV compared to existing heart valve substitutes were assessed from a healthcare perspective applying a 10-year time horizon. Improvements in performance of TEHV, divided in durability, thrombogenicity, and infection resistance, were explored to estimate quality-adjusted life years (QALY) gain, cost reduction, headroom, and budget impact associated with TEHV.
RESULTS: Five-year freedom from re-intervention after RVOTR with existing heart valve substitutes was 46.1% in patients â€2 years old and 81.1% in patients >2 years old. Improvements in durability had the highest impact on QALYs and costs. In the âimproved TEHV performanceâ scenario (durabilityâ„5 years and -50% other valve-related events), QALY gain was 0.074 and cost reduction was âŹ10,378 per patient, translating to maximum additional costs of âŹ11,856 per TEHV compared to existing heart valve substitutes.
CONCLUSIONS: This study showed that there is room for improvement in clinical outcomes in children requiring RVOTR. If TEHV result in improved clinical outcomes, they are expected to be costeffective compared to existing heart valve substitutes
The Utility of High-Resolution Melting Analysis of SNP Nucleated PCR AmpliconsâAn MLST Based Staphylococcus aureus Typing Scheme
High resolution melting (HRM) analysis is gaining prominence as a method for discriminating DNA sequence variants. Its advantage is that it is performed in a real-time PCR device, and the PCR amplification and HRM analysis are closed tube, and effectively single step. We have developed an HRM-based method for Staphylococcus aureus genotyping. Eight single nucleotide polymorphisms (SNPs) were derived from the S. aureus multi-locus sequence typing (MLST) database on the basis of maximized Simpson's Index of Diversity. Only GâA, GâT, CâA, CâT SNPs were considered for inclusion, to facilitate allele discrimination by HRM. In silico experiments revealed that DNA fragments incorporating the SNPs give much higher resolving power than randomly selected fragments. It was shown that the predicted optimum fragment size for HRM analysis was 200 bp, and that other SNPs within the fragments contribute to the resolving power. Six DNA fragments ranging from 83 bp to 219 bp, incorporating the resolution optimized SNPs were designed. HRM analysis of these fragments using 94 diverse S. aureus isolates of known sequence type or clonal complex (CC) revealed that sequence variants are resolved largely in accordance with G+C content. A combination of experimental results and in silico prediction indicates that HRM analysis resolves S. aureus into 268 âmelt typesâ (MelTs), and provides a Simpson's Index of Diversity of 0.978 with respect to MLST. There is a high concordance between HRM analysis and the MLST defined CCs. We have generated a Microsoft Excel key which facilitates data interpretation and translation between MelT and MLST data. The potential of this approach for genotyping other bacterial pathogens was investigated using a computerized approach to estimate the densities of SNPs with unlinked allelic states. The MLST databases for all species tested contained abundant unlinked SNPs, thus suggesting that high resolving power is not dependent upon large numbers of SNPs
Diffuse large B-cell non-Hodgkin lymphomas: the clinical relevance of histological subclassification
In the REAL classification the diffuse large B-cell non-Hodgkin lymphomas (NHL) are grouped together, because subclassifications are considered to lack both reproducibility and clinical significance. Others, however, claim that patients with an immunoblastic NHL have a worse prognosis than patients with other types of diffuse large B-cell NHL. Therefore, we investigated the prognostic and clinical significance of histological subclassification of diffuse large B-cell NHL in a uniformly treated series of patients. For this retrospective study, all patients diagnosed as having an immunoblastic (IB) B-cell NHL by the Lymphoma Review Panel of the Comprehensive Cancer Center Amsterdam (CCCA) between 1984 and 1994, and treated according to the guidelines of the CCCA, were analysed. Patients with a centroblastic polymorphic subtype (CB-Poly) or centroblastic (CB) NHL by the Lymphoma Review Panel who were treated in the Netherlands Cancer Institute during the same period according to CCCA guidelines were used as reference groups. All patients' records were reviewed. Clinical parameters at presentation, kind of therapy and clinical outcome were recorded. All available histological slides were separately reviewed by two haemato-pathologists. One hundred and seventy-seven patients were included in the study: 36 patients (20.3%) with an IB NHL, 69 patients (39%) with a CB-Poly NHL and 72 patients (40.7%) with a CB NHL. The patients with an IB NHL tended to be older and presented more often with stage I or II and one extranodal site than patients with a CB and CB-Poly NHL. None of the subtypes showed a clear preference for localization in a particular site. The patients with IB or CB-Poly NHL showed a significantly worse prognosis than patients with CB NHL, with a 5-year overall survival for patients with CB NHL of 56.3% and for patients with IB or CB-Poly NHL 39.1% and 41.6% respectively. The 5-year disease free survival was 53.2% for the patients with CB, 32% for the patients with CB-Poly and 26.9% for the patients with IB NHL. A multivariate analysis showed that histological subtyping was of prognostic significance independent of the International Prognostic Index. This finding merits further exploration in prospective studies in order to judge the value of subclassification of large B-cell NHL as a guideline in therapy choice. © 1999 Cancer Research Campaig
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