12,098 research outputs found
Finely integrated media for language learning
FLUENT, an immersive foreign‐language learning environment, was developed without recourse to hypermedia techniques. Nevertheless, if one accepts the premisses, proposed in this paper, on which the idea of hypermedia has been constructed, FLUENT shows a strong relationship with it. The paper discusses this relationship after attempting to distil the essence of educational hypermedia, and after presenting a taxonomy of media for language learning
Practical method for balancing airplane moments
The present contribution is the sequel to a paper written by Messrs. R. Fuchs, L. Hopf, and H. Hamburger, and proposes to show that the methods therein contained can be practically utilized in computations. Furthermore, the calculations leading up to the diagram of moments for three airplanes, whose performance in war service gave reason for complaint, are analyzed. Finally, it is shown what conclusions can be drawn from the diagram of moments with regard to the defects in these planes and what steps may be taken to remedy them
An illusion induced by an illusion -perceptual filling-in of coloured negative afterimages
Visual filling-in relates to a perceptual phenomenon in which a stimulus pattern apparently undergoes dynamic changes assuming an attribute such as colour, texture, or brightness from the surround. This perceptual completion effect has up to now been shown only for real images. Here, we present filling-in in negative afterimages, a phenomenon not yet reported. Using coloured disk-ring patterns for stimuli, we demonstrate that afterimage filling-in arises independently, and is not simply a replica of filling-in observed in real images. Such filling-in does not occur when the afterimage is elicited dichoptically, suggesting its emergence within the monocular visual pathway. In this way, our findings indicate that filling-in under certain conditions may derive from an active neural mechanism located at low levels of the visual pathway
Optical Theorem and the Inversion of Cross Section Data for Atom Scattering from Defects on Surfaces
The information content and properties of the cross section for atom
scattering from a defect on a flat surface are investigated. Using the Sudden
approximation, a simple expression is obtained that relates the cross section
to the underlying atom/defect interaction potential. An approximate inversion
formula is given, that determines the shape function of the defect from the
scattering data. Another inversion formula approximately determines the
potential due to a weak corrugation in the case of substitutional disorder. An
Optical Theorem, derived in the framework of the Sudden approximation, plays a
central role in deriving the equations that conveniently relate the interaction
potential to the cross section. Also essential for the result is the
equivalence of the operational definition for the cross section for scattering
by a defect, given by Poelsema and Comsa, and the formal definition from
quantum scattering theory. This equivalence is established here. The inversion
result is applied to determine the shape function of an Ag atom on Pt(111) from
scattering data.Comment: 29 pages, 9 Postscript figures, more info available at
http://www.fh.huji.ac.il/~dan
Fractal Dimension of Disordered Submonolayers: Determination from He Scattering Data
We propose a novel method to measure the fractal dimension of a submonolayer
metal adatom system grown under conditions of limited diffusivity on a surface.
The method is based on measuring the specular peak attenuation of He atoms
scattered from the surface, as a function of incidence energy. The (Minkowski)
fractal dimension thus obtained is that of contours of constant electron
density of the adatom system. Simulation results are presented, based on
experimental data. A coverage dependent fractal dimension is found from a
two-decade wide scaling regime.Comment: 12 pages, 4 figures, replaced with revised version. More info
available at http://www.fh.huji.ac.il/~dani/ . Chem. Phys. Lett., in pres
Motor recovery following capsular stroke
The functional anatomy of motor recovery was studied by assessing motor function quantitatively in 23 patients following capsular or striatocapsular stroke. While selective basal ganglia lesions (caudate and/or putamen exclusively) did not affect voluntary movements of the extremities, lesions of the anterior (plus caudate/putamen) or posterior limb of the internal capsule led to an initially severe motor impairment followed by excellent recovery, hand function included. In contrast, lesions of the posterior limb of the internal capsule in combination with damage to lateral thalamus compromised motor outcome. In experimental tracing of the topography of the internal capsule in macaque monkeys, we found axons of primary motor cortex passing through the middle third of the posterior limb of the internal capsule. Axons of premotor cortex (dorsolateral and post-arcuate area 6) passed through the capsular genu, and those of supplementary motor area (mesial area 6) through the anterior limb. Small capsular lesion can therefore disrupt the output of functionally and anatomically distinct motor areas selectively. The clinically similar motor deficits with a similar course of functional restitution following disruption of these different descending motor pathways indicate a parallel operation of cortical motor areas. They may have the further capability of substituting each other functionally in the process of recovery from hemiparesis
Limited Range Fractality of Randomly Adsorbed Rods
Multiple resolution analysis of two dimensional structures composed of
randomly adsorbed penetrable rods, for densities below the percolation
threshold, has been carried out using box-counting functions. It is found that
at relevant resolutions, for box-sizes, , between cutoffs given by the
average rod length and the average inter-rod distance $r_1$, these
systems exhibit apparent fractal behavior. It is shown that unlike the case of
randomly distributed isotropic objects, the upper cutoff $r_1$ is not only a
function of the coverage but also depends on the excluded volume, averaged over
the orientational distribution. Moreover, the apparent fractal dimension also
depends on the orientational distributions of the rods and decreases as it
becomes more anisotropic. For box sizes smaller than the box counting
function is determined by the internal structure of the rods, whether simple or
itself fractal. Two examples are considered - one of regular rods of one
dimensional structure and rods which are trimmed into a Cantor set structure
which are fractals themselves. The models examined are relevant to adsorption
of linear molecules and fibers, liquid crystals, stress induced fractures and
edge imperfections in metal catalysts. We thus obtain a distinction between two
ranges of length scales: where the internal structure of the
adsorbed objects is probed, and where their distribution is
probed, both of which may exhibit fractal behavior. This distinction is
relevant to the large class of systems which exhibit aggregation of a finite
density of fractal-like clusters, which includes surface growth in molecular
beam epitaxy and diffusion-limited-cluster-cluster-aggregation models.Comment: 10 pages, 7 figures. More info available at
http://www.fh.huji.ac.il/~dani/ or
http://www.fiz.huji.ac.il/staff/acc/faculty/biham or
http://chem.ch.huji.ac.il/employee/avnir/iavnir.htm . Accepted for
publication in J. Chem. Phy
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