42,941 research outputs found
Comparison of beam generation techniques using a phase only spatial light modulator
Whether in art or for QR codes, images have proven to be
both powerful and efficient carriers of information. Spatial light modulators
allow an unprecedented level of control over the generation of optical fields
by using digital holograms. There is no unique way of obtaining a desired
light pattern however, leaving many competing methods for hologram
generation. In this paper, we test six hologram generation techniques
in the creation of a variety of modes as well as a photographic image:
rating the methods according to obtained mode quality and power. All
techniques compensate for a non-uniform mode profile of the input laser
and incorporate amplitude scaling. We find that all methods perform well
and stress the importance of appropriate spatial filtering. We expect these
results to be of interest to those working in the contexts of microscopy,
optical trapping or quantum image creation
No-reference image quality assessment through the von Mises distribution
An innovative way of calculating the von Mises distribution (VMD) of image
entropy is introduced in this paper. The VMD's concentration parameter and some
fitness parameter that will be later defined, have been analyzed in the
experimental part for determining their suitability as a image quality
assessment measure in some particular distortions such as Gaussian blur or
additive Gaussian noise. To achieve such measure, the local R\'{e}nyi entropy
is calculated in four equally spaced orientations and used to determine the
parameters of the von Mises distribution of the image entropy. Considering
contextual images, experimental results after applying this model show that the
best-in-focus noise-free images are associated with the highest values for the
von Mises distribution concentration parameter and the highest approximation of
image data to the von Mises distribution model. Our defined von Misses fitness
parameter experimentally appears also as a suitable no-reference image quality
assessment indicator for no-contextual images.Comment: 29 pages, 11 figure
Engineering data compendium. Human perception and performance. User's guide
The concept underlying the Engineering Data Compendium was the product of a research and development program (Integrated Perceptual Information for Designers project) aimed at facilitating the application of basic research findings in human performance to the design and military crew systems. The principal objective was to develop a workable strategy for: (1) identifying and distilling information of potential value to system design from the existing research literature, and (2) presenting this technical information in a way that would aid its accessibility, interpretability, and applicability by systems designers. The present four volumes of the Engineering Data Compendium represent the first implementation of this strategy. This is the first volume, the User's Guide, containing a description of the program and instructions for its use
Measurement of Source Star Colors with the K2C9-CFHT Multi-color Microlensing Survey
K2 Campaign 9 (K2C9) was the first space-based microlensing parallax survey
capable of measuring microlensing parallaxes of free-floating planet candidate
microlensing events. Simultaneous to K2C9 observations we conducted the K2C9
Canada-France-Hawaii Telescope Multi-Color Microlensing Survey (K2C9-CFHT MCMS)
in order to measure the colors of microlensing source stars to improve the
accuracy of K2C9's parallax measurements. We describe the difference imaging
photometry analysis of the K2C9-CFHT MCMS observations, and present the
project's first data release. This includes instrumental difference flux
lightcurves of 217 microlensing events identified by other microlensing
surveys, reference image photometry calibrated to PanSTARRS data release 1
photometry, and tools to convert between instrumental and calibrated flux
scales. We derive accurate analytic transformations between the PanSTARRS
bandpasses and the Kepler bandpass, as well as angular diameter-color relations
in the PanSTARRS bandpasses. To demonstrate the use of our data set, we analyze
ground-based and K2 data of a short timescale microlensing event,
OGLE-2016-BLG-0795. We find the event has a timescale ~days and microlens parallax or , subject to the standard satellite parallax degeneracy. We argue that the
smaller value of the parallax is more likely, which implies that the lens is
likely a stellar-mass object in the Galactic bulge as opposed to a
super-Jupiter mass object in the Galactic disk.Comment: Submitted to PAS
A new method to determine multi-angular reflectance factor from lightweight multispectral cameras with sky sensor in a target-less workflow applicable to UAV
A new physically based method to estimate hemispheric-directional reflectance
factor (HDRF) from lightweight multispectral cameras that have a downwelling
irradiance sensor is presented. It combines radiometry with photogrammetric
computer vision to derive geometrically and radiometrically accurate data
purely from the images, without requiring reflectance targets or any other
additional information apart from the imagery. The sky sensor orientation is
initially computed using photogrammetric computer vision and revised with a
non-linear regression comprising radiometric and photogrammetry-derived
information. It works for both clear sky and overcast conditions. A
ground-based test acquisition of a Spectralon target observed from different
viewing directions and with different sun positions using a typical
multispectral sensor configuration for clear sky and overcast showed that both
the overall value and the directionality of the reflectance factor as reported
in the literature were well retrieved. An RMSE of 3% for clear sky and up to 5%
for overcast sky was observed
AstraLux: the Calar Alto Lucky Imaging Camera
AstraLux is the Lucky Imaging camera for the Calar Alto 2.2-m telescope,
based on an electron-multiplying high speed CCD. By selecting only the best
1-10% of several thousand short exposure frames, AstraLux provides nearly
diffraction limited imaging capabilities in the SDSS i' and z' filters over a
field of view of 24x24 arcseconds. By choosing commercially available
components wherever possible, the instrument could be built in short time and
at comparably low cost. We present the instrument design, the data reduction
pipeline, and summarise the performance and characteristicsComment: 12 pages, 7 figures, to appear in "Ground-based and Airborne
Instrumentation for Astronomy II" SPIE conference, Marseille, 23-28 June 200
Deformation compatibility in a single crystalline Ni superalloy
Deformation in materials is often complex and requires rigorous understanding to predict engineering component lifetime. Experimental understanding of deformation requires utilization of advanced characterization techniques, such as high spatial resolution digital image correlation (HR-DIC) and high angular resolution electron backscatter diffraction (HR-EBSD), combined with clear interpretation of their results to understand how a material has deformed. In this study, we use HR-DIC and HR-EBSD to explore the mechanical behaviour of a single-crystal nickel alloy and to highlight opportunities to understand the complete deformations state in materials. Coupling of HR-DIC and HR-EBSD enables us to precisely focus on the extent which we can access the deformation gradient, F, in its entirety and uncouple contributions from elastic deformation gradients, slip and rigid body rotations. Our results show a clear demonstration of the capabilities of these techniques, found within our experimental toolbox, to underpin fundamental mechanistic studies of deformation in polycrystalline materials and the role of microstructure
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White paper â On the use of LiDAR data at AmeriFlux sites
Our aim is to inform the AmeriFlux community on existing and upcoming LiDAR technologies (atmospheric Doppler
or Raman LiDAR often deployed at flux sites are not considered here), how it is currently used at flux sites, and how
we believe it could, in the future, further contribute to the AmeriFlux vision. Heterogeneity in vegetation and ground
properties at various spatial scales is omnipresent at flux sites, and 3D mapping of canopy, understory, and ground
surface can help move the science forward
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