39,429 research outputs found
Studies of atmospheric refraction effects on laser data
The refraction effect from three perspectives was considered. An analysis of the axioms on which the accepted correction algorithms were based was the first priority. The integrity of the meteorological measurements on which the correction model is based was also considered and a large quantity of laser observations was processed in an effort to detect any serious anomalies in them. The effect of refraction errors on geodetic parameters estimated from laser data using the most recent analysis procedures was the focus of the third element of study. The results concentrate on refraction errors which were found to be critical in the eventual use of the data for measurements of crustal dynamics
A fast GPU Monte Carlo Radiative Heat Transfer Implementation for Coupling with Direct Numerical Simulation
We implemented a fast Reciprocal Monte Carlo algorithm, to accurately solve
radiative heat transfer in turbulent flows of non-grey participating media that
can be coupled to fully resolved turbulent flows, namely to Direct Numerical
Simulation (DNS). The spectrally varying absorption coefficient is treated in a
narrow-band fashion with a correlated-k distribution. The implementation is
verified with analytical solutions and validated with results from literature
and line-by-line Monte Carlo computations. The method is implemented on GPU
with a thorough attention to memory transfer and computational efficiency. The
bottlenecks that dominate the computational expenses are addressed and several
techniques are proposed to optimize the GPU execution. By implementing the
proposed algorithmic accelerations, a speed-up of up to 3 orders of magnitude
can be achieved, while maintaining the same accuracy
Quantitative studies of nucleic acid in the cell by micro-spectrophotometry I. The critique and improvement of the microspectrophotometry
Some critical experiments have been carried out on the microspectrophotometry using the lymphocytes of a mouse, stained with Feulgen reaction, revealing that most reliable value can be attained by illuminating the material with a small spot-light and integrating the area surrounded by the extinction curve drawn by tracing along the diameter of the smeared and fixed cell.</p
Determining the Phase and Amplitude Distortion of a Wavefront using a Plenoptic Sensor
We have designed a plenoptic sensor to retrieve phase and amplitude changes
resulting from a laser beam's propagation through atmospheric turbulence.
Compared with the commonly restricted domain of (-pi, pi) in phase
reconstruction by interferometers, the reconstructed phase obtained by the
plenoptic sensors can be continuous up to a multiple of 2pi. When compared with
conventional Shack-Hartmann sensors, ambiguities caused by interference or low
intensity, such as branch points and branch cuts, are less likely to happen and
can be adaptively avoided by our reconstruction algorithm. In the design of our
plenoptic sensor, we modified the fundamental structure of a light field camera
into a mini Keplerian telescope array by accurately cascading the back focal
plane of its object lens with a microlens array's front focal plane and
matching the numerical aperture of both components. Unlike light field cameras
designed for incoherent imaging purposes, our plenoptic sensor operates on the
complex amplitude of the incident beam and distributes it into a matrix of
images that are simpler and less subject to interference than a global image of
the beam. Then, with the proposed reconstruction algorithms, the plenoptic
sensor is able to reconstruct the wavefront and a phase screen at an
appropriate depth in the field that causes the equivalent distortion on the
beam. The reconstructed results can be used to guide adaptive optics systems in
directing beam propagation through atmospheric turbulence. In this paper we
will show the theoretical analysis and experimental results obtained with the
plenoptic sensor and its reconstruction algorithms.Comment: This article has been accepted by JOSA
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