70 research outputs found
Can contrast-response functions indicate visual processing levels?
YesMany visual effects are believed to be processed at several functional and anatomical levels
of cortical processing. Determining if and how the levels contribute differentially to these effects is a
leading problem in visual perception and visual neuroscience. We review and analyze a combination
of extant psychophysical findings in the context of neurophysiological and brain-imaging results.
Specifically using findings relating to visual illusions, crowding, and masking as exemplary cases, we
develop a theoretical rationale for showing how relative levels of cortical processing contributing
to these effects can already be deduced from the psychophysically determined functions relating
respectively the illusory, crowding and masking strengths to the contrast of the illusion inducers, of
the flankers producing the crowding, and of the mask. The wider implications of this rationale show
how it can help to settle or clarify theoretical and interpretive inconsistencies and how it can further
psychophysical, brain-recording and brain-imaging research geared to explore the relative functional
and cortical levels at which conscious and unconscious processing of visual information occur. Our
approach also allows us to make some specific predictions for future studies, whose results will
provide empirical tests of its validity
Effect of annealing on the hyperfine interaction in InAs/GaAs quantum dots
The hyperfine interaction of an electron with nuclei in the annealed
self-assembled InAs/GaAs quantum dots is theoretically analyzed. For this
purpose, the annealing process, and energy structure of the quantum dots are
numerically modeled. The modeling is verified by comparison of the calculated
optical transitions and of the experimental data on photoluminescence for set
of the annealed quantum dots. The localization volume of the electron in the
ground state and the partial contributions of In, Ga, and As nuclei to the
hyperfine interaction are calculated as functions of the annealing temperature.
It is established that the contribution of indium nuclei into the hyperfine
interaction becomes predominant up to high annealing temperatures (T = 980 C)
when the In content in the quantum dots does not exceed 25%. Effect of the
nuclear spin fluctuations on the electron spin polarization is numerically
modeled. Effective field of the fluctuations is found to be in good agreement
with experimental data available
Photometric variability of young brown dwarfs in the sigma Orionis open cluster
We have carried out multi-epoch, time-series differential I-band photometry
of a large sample of objects in the south-east region of the young (~3 Myr),
nearby (~350 pc) sigma Orionis open cluster. A field of ~1000 arcmin^2 was
monitored during four nights over a period of two years. Using this dataset, we
have studied the photometric variability of twenty-eight brown dwarf cluster
candidates with masses ranging from the stellar-substellar boundary down to the
planetary-mass domain. We have found that about 50% of the sample show
photometric variability on timescales from less than one hour to several days
and years. The amplitudes of the I-band light curves range from less than 0.01
up to ~0.4 magnitudes. A correlation between the near-infrared excess in the
K_s band, strong Halpha emission and large-amplitude photometric variation is
observed. We briefly discuss how these results may fit the different scenarios
proposed to explain the variability of cool and ultracool dwarfs (i.e. magnetic
spots, patchy obscuration by dust clouds, surrounding accretion discs and
binarity). Additionally, we have determined tentative rotational periods in the
range 3 to 40 h for three objects with masses around 60 M_Jup, and the
rotational velocity of 14+/-4 km/s for one of them.Comment: Accepted for publication in A&
The interaction of homeostatic and circadian regulation of sleepiness depends on a PER3 polymorphism
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