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291.
The objects-first strategy to teaching programming has prevailed over the imperative-first and functional-first strategies during the last decade. However, the objects-first strategy has created added difficulties to both the teaching and learning of programming. In an attempt to confront these difficulties and support the objects-first strategy we developed a novel programming environment, objectKarel, which uses the language Karel++. The design of objectKarel was based on the results of the extended research that has been carried out about novice programmers. What differentiates it from analogous environments is the fact that it combines features that have been used solely in them: incorporated e-lessons and hands-on activities; an easy to use structure editor for developing/editing programs; program animation; explanatory visualization; highly informative and friendly error messages; recordability. In this paper, we present the didactic rationale that dictated the design of objectKarel and the features of the environment, including the e-lessons. In addition, we present the results from the use of objectKarel in the classroom and the results of the students’ assessment of the environment. 相似文献
292.
293.
N. Guskos J. Typek G. Zolnierkiewicz K. Wardal A. Guskos P. Berczynski D. Petridis 《Materials Science-Poland》2013,31(4):587-594
Two composites consisting of γ-Fe2O3 (maghemite) nanoparticles covered by two different oxygen-based free radicals derived from a 4-(methylamino)phenol sulphate and 8-hydroxy-1,3,6-trisulfonic trisodium salt acid were prepared and investigated by the magnetic resonance method in the 4–300 K range. Both composites displayed broad and very intense ferromagnetic resonance (FMR) lines originating from γ-Fe2O3 agglomerated nanoparticles. The FMR spectrum was fitted satisfactorily at each temperature by two Landau-Lifshitz functions reflecting the existence of magnetic anisotropy in the investigated system. The temperature dependence of the obtained FMR parameters (resonance field, linewidth, integrated intensity) was studied and the results were interpreted in terms of magnetic interactions between free radicals and nanoparticle agglomerates. A comparison with previously studied similar systems containing maghemite nanoparticles was made and conclusions about the role of free radicals were drawn. 相似文献
294.
We demonstrate theoretically that electric dipole-forbidden atomic transitions can be excited by the interaction of the quadrupole moment of the transition with the electric near-field in the vicinity of an illuminated periodic array of core–shell metallic nanoparticles via surface-plasmon excitation. The rate of the quadrupole transition is enhanced by nine orders of magnitude relative to the illumination of the atom by a plane wave rendering the transition experimentally observable. At the same time, the enhancement of the quadrupole transition rate means an enhancement of the quadrupole force at the same level, enabling the subwavelength trapping of the atom at the optical near-field landscape. The calculations are based on rigorous electrodynamic calculations based on the layer-multiple-scattering theory for periodic nanostructures of spherical scatterers. The quadrupole transition is studied by means of electromagnetic multipole angular momentum theory which provides a closed formula for the corresponding atomic transition rate. 相似文献
295.
296.
Poulopoulos P Kapaklis V Politis C Schweiss P Fuchs D 《Journal of nanoscience and nanotechnology》2006,6(12):3867-3870
Nanoscale Ni films in the thickness range 15-500 nm were grown on various substrates, such as amorphous glass, single crystalline silicon and sapphire, and polycrystalline alumina, at a temperature of about 350 K by radio frequency magnetron sputtering. It is demonstrated, via X-ray diffraction and high-resolution transmission electron microscopy, that there is an Ar-gas pressure window that favors the growth of stable single-phase hexagonal nanocrystalline Ni films regardless of the film thickness and the kind of the substrate. At lower or higher Ar pressures the films grow in the regular face centered cubic phase of Ni. The structural habits are attributed to differences in the kinetic energy of the Ni atoms impinging on the substrates. Superconducting quantum interference device magnetometry measurements reveal that the hexagonal films show zero magnetic response down to liquid Helium temperature. This result is discussed with respect to earlier first principle calculations and to experimental results on Ni nanoparticles. 相似文献
297.
Vassilios S. Vassiliou Katharina Wassilew Donnie Cameron Ee Ling Heng Evangelia Nyktari George Asimakopoulos Anthony de Souza Shivraman Giri Iain Pierce Andrew Jabbour David Firmin Michael Frenneaux Peter Gatehouse Dudley J. Pennell Sanjay K. Prasad 《Magma (New York, N.Y.)》2018,31(1):101-113
Objectives
Our objectives involved identifying whether repeated averaging in basal and mid left ventricular myocardial levels improves precision and correlation with collagen volume fraction for 11 heartbeat MOLLI T 1 mapping versus assessment at a single ventricular level.Materials and methods
For assessment of T 1 mapping precision, a cohort of 15 healthy volunteers underwent two CMR scans on separate days using an 11 heartbeat MOLLI with a 5(3)3 beat scheme to measure native T 1 and a 4(1)3(1)2 beat post-contrast scheme to measure post-contrast T 1, allowing calculation of partition coefficient and ECV. To assess correlation of T 1 mapping with collagen volume fraction, a separate cohort of ten aortic stenosis patients scheduled to undergo surgery underwent one CMR scan with this 11 heartbeat MOLLI scheme, followed by intraoperative tru-cut myocardial biopsy. Six models of myocardial diffuse fibrosis assessment were established with incremental inclusion of imaging by averaging of the basal and mid-myocardial left ventricular levels, and each model was assessed for precision and correlation with collagen volume fraction.Results
A model using 11 heart beat MOLLI imaging of two basal and two mid ventricular level averaged T 1 maps provided improved precision (Intraclass correlation 0.93 vs 0.84) and correlation with histology (R 2 = 0.83 vs 0.36) for diffuse fibrosis compared to a single mid-ventricular level alone. ECV was more precise and correlated better than native T 1 mapping.Conclusion
T 1 mapping sequences with repeated averaging could be considered for applications of 11 heartbeat MOLLI, especially when small changes in native T 1/ECV might affect clinical management.298.
Numerical solution of yield viscoplastic fluid flow is hindered by the singularity inherent to the Herschel-Bulkley model.A finite difference method over the boundary-fitted orthogonal coordinate system is util-ized to investigate numerically the fully developed steady flow of non-Newtonian yield viscoplastic fluid through concentric and eccentric annuli.The fluid rheology is described with the Herschel-Bulkley model.The numerical simulation based on a continuous viscoplastic approach to the Herschel-Bulkley model is found in poor accordance with the experimental data on volumetric flow rate of a bentonite suspension.A strict mathematical model for Herschel-Bulkley fluid flow is established and the corresponding numerical procedures are proposed.However,only the case of flow of a Herschel-Bulkley fluid in a concentric annulus is resolved based on the presumed flow structure by using the common optimization technique.Possible flow structures in an eccentric annulus are pre-sumed,and further challenges in numerical simulation of the Herschel-Bulkley fluid flow are suggested. 相似文献
299.
A. Bakandritsos A. B. Bourlinos V. Tzitzios N. Boukos E. Devlin T. Steriotis V. Kouvelos D. Petridis 《Advanced functional materials》2007,17(8):1409-1416
Aqueous solutions of sodium carboxymethyl cellulose are used for the morphosynthesis of spherical and wire‐shaped biopolymer networks, in which Fe3+ cations serve as a crosslinking and hardening agent. Their morphology remains intact upon drying, resulting in monolithic beads (1 mm) and wires (ca. 80 μm), which are exploited as reaction vessels to pre‐encapsulate poly(ethylene glycol) 400 (PEG 400) and cobalt cations. A solid‐state reaction in an inert atmosphere at 600 °C affords porous carbonaceous xerogels, macroscopically shaped as beads or wires and decorated with nanocrystalline magnetic iron oxide, metallic iron, or iron–cobalt alloy particles, thus imparting magnetic properties to the products. As such the reduction of Fe3+ species to α‐Fe nanoparticles can be achieved without H2 treatment, since poly(ethylene glycol) serves as a reducing agent and the encapsulated Co2+ aids in the subsequent growth of the metallic iron particles. Particularly interesting are the magnetic properties of the carbon–α‐Fe composite, in which the size of the magnetic particles, estimated near the boundaries of the single magnetic domain, gives rise to increased coercivity compared with that of bulk iron. 相似文献
300.
Vassilios V. Digalakis Vinay K. Ingle Dimitris G. Manolakis 《Multidimensional Systems and Signal Processing》1993,4(4):307-329
In this article, we apply three-dimensional (3-D) linear least-squares (LS) prediction technique to the processing of digital subtraction angiography (DSA) image sequences. The main goal of this processing is the cancellation of motion artifacts, which is a visual structured noise that appears in current DSA images. We address two important issues with this new technique: first the misregistration between the mask and the contrast image and, second, the temporal filtering of DSA image sequence. Instead of treating these two issues separately, as conventional DSA methods do, we combine them into a 3-D LS prediction problem. Based on this approach, we develop a new efficient algorithm for the solution of normal equations. The algorithm is based on a new property of T
n
(Toeplitz to then) matrices that we prove. In order to match the image sequence physical characteristics, we further optimize practical parameters of this algorithm. Actual patient data is used for the evaluation of this new technique. Results show a significant improvement over the existing methods. 相似文献