27,482 research outputs found
Combining simultaneous with temporal masking
Simultaneous and temporal masking are two frequently used techniques in psychology and vision science. Although there are many studies and theories related to each masking technique, there are no systematic investigations of their mutual relationship, even though both techniques are often applied together. Here, the authors show that temporal masking can both undo and enhance the deteriorating effects of simultaneous masking depending on the stimulus onset asynchrony between the simultaneous and temporal masks. For the task and stimuli used in this study, temporal masking was largely unaffected by the properties of the simultaneous mask. In contrast, simultaneous masking seems to depend strongly on spatial grouping and was strongly affected by the properties of the temporal mask. These findings help to identify the nature of both temporal and simultaneous masking and promote understanding of the role of spatial and temporal grouping in visual perception
The VORTEX project: first results and perspectives
(abridged) Vortex coronagraphs are among the most promising solutions to
perform high contrast imaging at small angular separations. They feature a very
small inner working angle, a clear 360 degree discovery space, have
demonstrated very high contrast capabilities, are easy to implement on
high-contrast imaging instruments, and have already been extensively tested on
the sky. Since 2005, we have been designing, developing and testing an
implementation of the charge-2 vector vortex phase mask based on concentric
subwavelength gratings, referred to as the Annular Groove Phase Mask (AGPM).
Science-grade mid-infrared AGPMs were produced in 2012 for the first time,
using plasma etching on synthetic diamond substrates. They have been validated
on a coronagraphic test bench, showing broadband peak rejection up to 500:1 in
the L band, which translates into a raw contrast of about at
. Three of them have now been installed on world-leading
diffraction-limited infrared cameras (VLT/NACO, VLT/VISIR and LBT/LMIRCam).
During the science verification observations with our L-band AGPM on NACO, we
observed the beta Pictoris system and obtained unprecedented sensitivity limits
to planetary companions down to the diffraction limit (). More recently,
we obtained new images of the HR 8799 system at L band during the AGPM first
light on LMIRCam. After reviewing these first results obtained with
mid-infrared AGPMs, we will discuss the short- and mid-term goals of the
on-going VORTEX project, which aims to improve the performance of our vortex
phase masks for future applications on second-generation high-contrast imagers
and on future extremely large telescopes (ELTs).Comment: To appear in SPIE proceedings vol. 914
SST/CRISP Observations of Convective Flows in a Sunspot Penumbra
Context. Recent discoveries of intensity correlated downflows in the interior
of a sunspot penumbra provide direct evidence for overturning convection,
adding to earlier strong indications of convection from filament dynamics
observed far from solar disk center, and supporting recent simulations of
sunspots.
Aims. Using spectropolarimetric observations obtained at a spatial resolution
approaching 0'.'1 with the Swedish 1-m Solar Telescope (SST) and its
spectropolarimeter CRISP, we investigate whether the convective downflows
recently discovered in the C i line at 538.03 nm can also be detected in the
wings of the Fe i line at 630.15 nm
Methods. We make azimuthal fits of the measured LOS velocities in the core
and wings of the 538 nm and 630 nm lines to disentangle the vertical and
horizontal flows. To investigate how these depend on the continuum intensity,
the azimuthal fits are made separately for each intensity bin. By using
spatially high-pass filtered measurements of the LOS component of the magnetic
field, the flow properties are determined separately for magnetic spines
(relatively strong and vertical field) and inter-spines (weaker and more
horizontal field).
Results. The dark convective downflows discovered recently in the 538.03 nm
line are evident also in the 630.15 nm line, and have similar strength. This
convective signature is the same in spines and inter-spines. However, the
strong radial (Evershed) outflows are found only in the inter-spines.
Conclusions. At the spatial resolution of the present SST/CRISP data, the
small-scale intensity pattern seen in continuum images is strongly related to a
convective up/down flow pattern that exists everywhere in the penumbra. Earlier
failures to detect the dark convective downflows in the interior penumbra can
be explained by inadequate spatial resolution in the observed data.Comment: Revised and expanded by 2.5 pages. Fig. 14 adde
High-Performance Shuffle Motor Fabricated by Vertical Trench Isolation Technology
Shuffle motors are electrostatic stepper micromotors that employ a built-in mechanical leverage to produce large output forces as well as high resolution displacements. These motors can generally move only over predefined paths that served as driving electrodes. Here, we present the design, modeling and experimental characterization of a novel shuffle motor that moves over an unpatterned, electrically grounded surface. By combining the novel design with an innovative micromachining method based on vertical trench isolation, we have greatly simplified the fabrication of the shuffle motors and significantly improved their overall performance characteristics and reliability. Depending on the propulsion voltage, our motor with external dimensions of 290 μm × 410 mm displays two distinct operational modes with adjustable step sizes varying respectively from 0.6 to 7 nm and from 49 to 62 nm. The prototype was driven up to a cycling frequency of 80 kHz, showing nearly linear dependence of its velocity with frequency and a maximum velocity of 3.6 mm/s. For driving voltages of 55 V, the device had a maximum travel range of ±70 μm and exhibited an output force of 1.7 mN, resulting in the highest force and power densities reported so far for an electrostatic micromotor. After five days of operation, it had traveled a cumulative distance of more than 1.5 km in 34 billion steps without noticeable deterioration in performance.\u
Solar Magnetic Feature Detection and Tracking for Space Weather Monitoring
We present an automated system for detecting, tracking, and cataloging
emerging active regions throughout their evolution and decay using SOHO
Michelson Doppler Interferometer (MDI) magnetograms. The SolarMonitor Active
Region Tracking (SMART) algorithm relies on consecutive image differencing to
remove both quiet-Sun and transient magnetic features, and region-growing
techniques to group flux concentrations into classifiable features. We
determine magnetic properties such as region size, total flux, flux imbalance,
flux emergence rate, Schrijver's R-value, R* (a modified version of R), and
Falconer's measurement of non-potentiality. A persistence algorithm is used to
associate developed active regions with emerging flux regions in previous
measurements, and to track regions beyond the limb through multiple solar
rotations. We find that the total number and area of magnetic regions on disk
vary with the sunspot cycle. While sunspot numbers are a proxy to the solar
magnetic field, SMART offers a direct diagnostic of the surface magnetic field
and its variation over timescale of hours to years. SMART will form the basis
of the active region extraction and tracking algorithm for the Heliophysics
Integrated Observatory (HELIO)
Evaluation of CNN-based Single-Image Depth Estimation Methods
While an increasing interest in deep models for single-image depth estimation
methods can be observed, established schemes for their evaluation are still
limited. We propose a set of novel quality criteria, allowing for a more
detailed analysis by focusing on specific characteristics of depth maps. In
particular, we address the preservation of edges and planar regions, depth
consistency, and absolute distance accuracy. In order to employ these metrics
to evaluate and compare state-of-the-art single-image depth estimation
approaches, we provide a new high-quality RGB-D dataset. We used a DSLR camera
together with a laser scanner to acquire high-resolution images and highly
accurate depth maps. Experimental results show the validity of our proposed
evaluation protocol
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