10,966 research outputs found
The effects of belongingness on the Simultaneous Lightness Contrast: A virtual reality study
Simultaneous Lightness Contrast (SLC) is the phenomenon whereby a grey patch on a dark background appears lighter than an equal patch on a light background. Interestingly, the lightness difference between these patches undergoes substantial augmentation when the two backgrounds are patterned, thereby forming the articulated-SLC display. There are two main interpretations of these phenomena: The midlevel interpretation maintains that the visual system groups the luminance within a set of contiguous frameworks, whilst the high-level one claims that the visual system splits the luminance into separate overlapping layers corresponding to separate physical contributions. This research aimed to test these two interpretations by systematically manipulating the viewing distance and the horizontal distance between the backgrounds of both the articulated and plain SLC displays. An immersive 3D Virtual Reality system was employed to reproduce identical alignment and distances, as well as isolating participants
from interfering luminance. Results showed that reducing the viewing distance resulted in increased contrast
in both the plain- and articulated-SLC displays and that, increasing the horizontal distance between the backgrounds resulted in decreased contrast in the articulated condition but increased contrast in the plain condition. These results suggest that a comprehensive lightness theory should combine the two interpretations
Behavior of nanoparticle clouds around a magnetized microsphere under magnetic and flow fields
When a micron-sized magnetizable particle is introduced into a suspension of
nanosized magnetic particles, the nanoparticles accumulate around the
microparticle and form thick anisotropic clouds extended in the direction of
the applied magnetic field. This phenomenon promotes colloidal stabilization of
bimodal magnetic suspensions and allows efficient magnetic separation of
nanoparticles used in bioanalysis and water purification. In the present work,
size and shape of nanoparticle clouds under the simultaneous action of an
external uniform magnetic field and the flow have been studied in details. In
experiments, dilute suspension of iron oxide nanoclusters (of a mean diameter
of 60 nm) was pushed through a thin slit channel with the nickel microspheres
(of a mean diameter of 50m) attached to the channel wall. The behavior of
nanocluster clouds was observed in the steady state using an optical
microscope. In the presence of strong enough flow, the size of the clouds
monotonically decreases with increasing flow speed in both longitudinal and
transverse magnetic fields. This is qualitatively explained by enhancement of
hydrodynamic forces washing the nanoclusters away from the clouds. In the
longitudinal field, the flow induces asymmetry of the front and the back
clouds. To explain the flow and the field effects on the clouds, we have
developed a simple model based on the balance of the stresses and particle
fluxes on the cloud surface. This model, applied to the case of the magnetic
field parallel to the flow, captures reasonably well the flow effect on the
size and shape of the cloud and reveals that the only dimensionless parameter
governing the cloud size is the ratio of hydrodynamic-to-magnetic forces - the
Mason number. At strong magnetic interactions considered in the present work
(dipolar coupling parameter ), the Brownian motion seems not to
affect the cloud behavior
A chip-scale integrated cavity-electro-optomechanics platform
We present an integrated optomechanical and electromechanical nanocavity, in
which a common mechanical degree of freedom is coupled to an ultrahigh-Q
photonic crystal defect cavity and an electrical circuit. The sys- tem allows
for wide-range, fast electrical tuning of the optical nanocavity resonances,
and for electrical control of optical radiation pressure back-action effects
such as mechanical amplification (phonon lasing), cooling, and stiffening.
These sort of integrated devices offer a new means to efficiently interconvert
weak microwave and optical signals, and are expected to pave the way for a new
class of micro-sensors utilizing optomechanical back-action for thermal noise
reduction and low-noise optical read-out.Comment: 11 pages, 7 figure
Interface Characteristics at an Organic/Metal Junction: Pentacene on Cu Stepped Surfaces
The adsorption of pentacene on Cu(221), Cu(511) and Cu(911) is investigated
using density functional theory (DFT) with the self-consistent inclusion of van
der Waals (vdW) interactions. Cu(211) is a vicinal of Cu(111) while Cu(511) and
(911) are vicinals of Cu(100). For all the three surfaces, we found pentacene
to prefer to adsorb parallel to the surface and near the steps. The addition of
vdW interactions resulted in an enhancement in adsorption energies, with
reference to the PBE functional, of around 2 eV. With vdWs inclusion, the
adsorption energies were found to be 2.98 eV, 3.20 eV and 3.49 eV for Cu(211),
Cu(511) and Cu(911) respectively. These values reflect that pentacene adsorbs
stronger on (100) terraces with a preference for larger terraces. The molecule
tilts upon adsorption with a small tilt angle on the (100) vicinals (about a
few degrees) as compared to a large one on Cu(221) where the tilt angle is
found to be about 20o. We find that the adsorption results in a net charge
transfer to the molecule of ~1 electron, for all surfaces.Comment: 11 pages, 4 figure
Facile synthesis of metal-free organic dyes featuring a thienylethynyl spacer for dye sensitized solar cells
In this article, we report the facile synthesis of metal-free dyes 6 and 7, their solution-based optical and redox properties and their use as sensitizers in dye-sensitized solar cells (DSSCs). Our studies indicate that the addition of the second thiophene unit in dye 7, decreases the oxidation and reduction potential and consequently the band gap of the molecule compared to 6. Furthermore, increasing the length of the conjugated spacer also affects on the properties of the DSSCs, with dye 7 providing a higher power conversion efficiency compared to 6 (η = 4.49 versus 3.23%)
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