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21.
Holland AE Engelbrecht MR Barentsz JO Heijstraten FM Goldfarb JW 《Magnetic resonance imaging》2002,20(3):261-269
The value of ECG-gated single-shot black-blood MR imaging for rapid visualization of the origin and course of the coronary arteries was investigated. The study population included 28 patients with known or suspected cardiac disease. ECG-gated single-shot black-blood MR acquisitions were acquired in the transverse, coronal, sagittal and LAO orientations, during free breathing and breath-holding. The origin of the left coronary artery was most frequently visualized in the coronal and LAO orientations and the origin of the right coronary artery was most frequently visualized in the LAO orientation. Overall, no significant difference was found for the visualization of the coronary artery segments and the overall image quality among acquisitions during breath-holding and free breathing. ECG-gated single-shot black-blood MR imaging (HASTE) appears to be a time-efficient and robust method for mapping of the entire coronary artery tree, without the need for breath-holding. The LAO orientation provides the most consistent visualization of the origins and major coronary artery segments. 相似文献
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We study the long-term average frequency as a function of the natural frequency for Kuramoto oscillators with periodic coefficients. Unlike the case for more general periodically forced oscillators, this function is never a "devil's staircase"; it may have plateaus at integer multiples of the forcing frequency, but we prove it is strictly increasing between these plateaus. The proof uses the fact that the flow maps for Kuramoto oscillators extend to M?bius transformations on the complex plane, and that M?bius transformations have particularly simple dynamics that rule out p∶q mode locking except in the case of fixed points (q=1). We also give a criterion for the degeneration of an integer plateau to a single point and use it to explain the absence of plateaus at even multiples of the collective frequency for a Kuramoto system with a bimodal frequency distribution. 相似文献
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A. Berezovski J. Engelbrecht G. A. Maugin 《Archive of Applied Mechanics (Ingenieur Archiv)》2000,70(10):694-706
Summary A novel approach to the modeling of thermoelastic wave propagation is presented, based on the thermodynamics of discrete
systems. The first novelty includes the representation of integral balance laws for thermoelasticity in terms of contact quantities
that describe the nonequilibrium state of elements. The next new aspect is a modification of the recently proposed wave-propagation
algorithm, which is used as a tool for determining the contact quantities in a finite-volume scheme for the numerical simulation
of two-dimensional thermoelastic wave propagation in inhomogeneous media. Such a modification is needed to provide the satisfaction
of the thermodynamic consistency conditions between adjacent discrete elements. Results of computations for certain test problems
show the efficiency and physical consistency of the algorithm.
Received 11 November 1999; accepted for publication 2 May 2000 相似文献
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Marietjie Lutz Lize Engelbrecht Angelique Laurie Nelisa Dyayiya 《International Journal of Polymer Analysis and Characterization》2018,23(4):300-312
Efficient characterization of the distribution of antimicrobial agents within a polymer matrix is of vital importance. Two antimicrobial agents, chitin nanowhiskers (ChNWs) and chitosan-based silver nanoparticles (CTSAgNPs), were produced and incorporated separately as well as combined into a poly(ethylene-co-vinyl alcohol) (EVOH) matrix by way of electrospinning. Correlative light and electron microscopy (CLEM) and energy dispersive X-ray mapping provided a holistic approach to visualize the distribution of the combinations of AgNPs and ChNWs within EVOH fibers. CLEM analysis revealed the tendency of the ChNWs to align themselves on the surface of the fibers, while the silver nanoparticles were localized inside the polymer matrix. 相似文献
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Zusammenfassung Untersucht wird die Elektrolyse flüssiger HF-SO2-Mischungen bei –30°C und verschiedenen Wassergehalten. Eine Gasentwicklung findet lediglich an der Anode statt, wobei Sulfurylfluorid als Hauptprodukt in einer Stromausbeute von 85% auftritt, während an der Kathode Schwefelabscheidung festgestellt wird. Bei hohen Wassergehalten im Elektrolyten unterbleibt diese Gasentwicklung, und es findet eine anodische Oxydation von schwefeliger Säure zu Schwefelsäure statt, die infolge des gleichzeitig vorhandenen Fluorwasserstoffes auch Fluorsulfonsäure entstehen läßt.Mit 1 Abbildung 相似文献
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A. Berezovski J. Engelbrecht A. Salupere K. Tamm T. Peets M. Berezovski 《International Journal of Solids and Structures》2013,50(11-12):1981-1990
The wave motion in micromorphic microstructured solids is studied. The mathematical model is based on ideas of Mindlin and governing equations are derived by making use of the Euler–Lagrange formalism. The same result is obtained by means of the internal variables approach. Actually such a model describes internal fields in microstructured solids under external loading and the interaction of these fields results in various physical effects. The emphasis of the paper is on dispersion analysis and wave profiles generated by initial or boundary conditions in a one-dimensional case. 相似文献
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ZDM – Mathematics Education - Growing use of the internet in educational contexts has been prominent in recent years. In this survey paper, we describe how the internet is transforming the... 相似文献