865 research outputs found
Von Bezold assimilation effect reverses in stereoscopic conditions
Lightness contrast and lightness assimilation are opposite phenomena: in contrast,
grey targets appear darker when bordering bright surfaces (inducers) rather than dark ones; in
assimilation, the opposite occurs. The question is: which visual process favours the occurrence
of one phenomenon over the other? Researchers provided three answers to this question. The
first asserts that both phenomena are caused by peripheral processes; the second attributes their
occurrence to central processes; and the third claims that contrast involves central processes,
whilst assimilation involves peripheral ones. To test these hypotheses, an experiment on an IT
system equipped with goggles for stereo vision was run. Observers were asked to evaluate the
lightness of a grey target, and two variables were systematically manipulated: (i) the apparent
distance of the inducers; and (ii) brightness of the inducers. The retinal stimulation was kept
constant throughout, so that the peripheral processes remained the same. The results show that
the lightness of the target depends on both variables. As the retinal stimulation was kept constant, we
conclude that central mechanisms are involved in both lightness contrast and lightness assimilation
Composition Operators and Endomorphisms
If is an inner function, then composition with induces an
endomorphism, , of that leaves
invariant. We investigate the structure of the
endomorphisms of and that implement
through the representations of and
in terms of multiplication operators on
and . Our analysis, which is based on work
of R. Rochberg and J. McDonald, will wind its way through the theory of
composition operators on spaces of analytic functions to recent work on Cuntz
families of isometries and Hilbert -modules
The Dirichlet-to-Robin Transform
A simple transformation converts a solution of a partial differential
equation with a Dirichlet boundary condition to a function satisfying a Robin
(generalized Neumann) condition. In the simplest cases this observation enables
the exact construction of the Green functions for the wave, heat, and
Schrodinger problems with a Robin boundary condition. The resulting physical
picture is that the field can exchange energy with the boundary, and a delayed
reflection from the boundary results. In more general situations the method
allows at least approximate and local construction of the appropriate reflected
solutions, and hence a "classical path" analysis of the Green functions and the
associated spectral information. By this method we solve the wave equation on
an interval with one Robin and one Dirichlet endpoint, and thence derive
several variants of a Gutzwiller-type expansion for the density of eigenvalues.
The variants are consistent except for an interesting subtlety of
distributional convergence that affects only the neighborhood of zero in the
frequency variable.Comment: 31 pages, 5 figures; RevTe
Modeling and characterization of the SPIDER half-wave plate
Spider is a balloon-borne array of six telescopes that will observe the
Cosmic Microwave Background. The 2624 antenna-coupled bolometers in the
instrument will make a polarization map of the CMB with approximately one-half
degree resolution at 145 GHz. Polarization modulation is achieved via a
cryogenic sapphire half-wave plate (HWP) skyward of the primary optic. We have
measured millimeter-wave transmission spectra of the sapphire at room and
cryogenic temperatures. The spectra are consistent with our physical optics
model, and the data gives excellent measurements of the indices of A-cut
sapphire. We have also taken preliminary spectra of the integrated HWP, optical
system, and detectors in the prototype Spider receiver. We calculate the
variation in response of the HWP between observing the CMB and foreground
spectra, and estimate that it should not limit the Spider constraints on
inflation
Personality trait development in midlife: exploring the impact of psychological turning points
This study examined long-term personality trait development in midlife and explored the impact of psychological turning points on personality change. Selfdefined psychological turning points reflect major changes in the ways people think or feel about an important part of their life, such as work, family, and beliefs about themselves and about the world. This study used longitudinal data from the Midlife in the US survey to examine personality trait development in adults aged 40–60 years. The Big Five traits were assessed in 1995 and 2005 by means of self-descriptive adjectives. Seven types of self-identified psychological turning points were obtained in 1995. Results indicated relatively high stability with respect to rankorders and mean-levels of personality traits, and at the same time reliable individual differences in change. This implies
that despite the relative stability of personality traits in the overall sample, some individuals show systematic deviations from the sample mean-levels. Psychological turning points in general showed very little influence on personality trait change, although some effects were found for specific types of turning points that warrant further research, such as discovering that a close friend or relative was a much better person than one thought they were
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