276 research outputs found

    Spatial coherence control and analysis via micromirror-based mixed-state ptychography

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    Flexible and fast control of the phase and amplitude of coherent light, enabled by digital micromirror devices (DMDs) and spatial light modulators (SLMs), has been a driving force for recent advances in optical tweezers, nonlinear microscopy, and wavefront shaping. In contrast, engineering spatially partially coherent light remains widely elusive due to the lack of tools enabling a joint analysis and control sequence. Here, we report an approach to coherence engineering that combines a quasi-monochromatic, thermal source and a DMD together with a ptychographic scanning microscope. The reported method opens up new routes to low-cost coherence control, with applications in micromanipulation, nanophotonics, and quantitative phase contrast imaging

    A three-dimensional heat and mass transport model for a tree within a forest

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    A three-dimensional computational tool was developed that simulates the heat and mass transfer interaction in a soil-root-stem system (SRSS) for a tree in a seasonally varying deciduous forest. The development of the SRSS model involved the modification and coupling of existing heat and mass transport tools to reproduce the three-dimensional diurnal internal and external temperatures, internal fluid distribution, and heat flow in the soil, roots, and stems. The model also required the development of a parallel Monte-Carlo algorithm to simulate the solar and environmental radiation regime consisting of sky and forest radiative effects surrounding the tree. The SRSS was tested, component-wise verified, and quantitatively compared with published observations. The SRSS was applied to simulate a tree in a dense temperate hardwood forest that included the calculations of surface heat flux and comparisons between cases with fluid flow transport and periods of zero flow. Results from the winter simulations indicate that the primary influence of temperature in the trunk is solar radiation and radiative energy from the soil and surrounding trees. Results from the summer simulation differed with previous results, indicating that sap flow in the trunk altered the internal temperature change with secondary effects attributed to the radiative energy from the soil and surrounding trees. Summer simulation results also showed that with sap flow, as the soil around the roots become unsaturated, the flow path for the roots will be changed to areas where the soil is still saturated with a corresponding increase in fluid velocity

    GaBoDS: The Garching-Bonn Deep Survey; IV. Methods for the Image reduction of multi-chip Cameras

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    We present our image processing system for the reduction of optical imaging data from multi-chip cameras. In the framework of the Garching Bonn Deep Survey (GaBoDS; Schirmer et al. 2003) consisting of about 20 square degrees of high-quality data from WFI@MPG/ESO 2.2m, our group developed an imaging pipeline for the homogeneous and efficient processing of this large data set. Having weak gravitational lensing as the main science driver, our algorithms are optimised to produce deep co-added mosaics from individual exposures obtained from empty field observations. However, the modular design of our pipeline allows an easy adaption to different scientific applications. Our system has already been ported to a large variety of optical instruments and its products have been used in various scientific contexts. In this paper we give a thorough description of the algorithms used and a careful evaluation of the accuracies reached. This concerns the removal of the instrumental signature, the astrometric alignment, photometric calibration and the characterisation of final co-added mosaics. In addition we give a more general overview on the image reduction process and comment on observing strategies where they have significant influence on the data quality.Comment: 34 pages, 33 figures; submitted to A&A main journa

    A Doppler Coherence Imaging Diagnostic for the Mega-Amp Spherical Tokamak

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    Developing a plasma exhaust solution suitable for future high power tokamaks is one of the major challenges facing the development of magnetic confinement fusion as a terrestrial energy source. In order to improve our understanding of the relevant physics, high quality experimental measurements of plasma dynamics in the scrape-off-layer (SOL) and divertor plasma regions are required. This thesis is concerned with the development of diagnostic instrumentation for measuring exhaust plasma flow: an important phenomenon with implications for the control of exhaust particles and heat as well as unwanted impurities. Coherence imaging spectroscopy (CIS) is a relatively new diagnostic technique which can be used to obtain time resolved 2D imaging of flows using the Doppler shifts of visible ion emission lines. The technique makes use of an imaging polarization interferometer and is based on the concept of Fourier transform spectroscopy. The principle advantages of this over other flow measurement techniques are the very large amount of spatial information collected, and the simple relationship between the measured quantities and spatially varying flows in the plasma. This thesis presents the development of, and first results from, a CIS ion flow diagnostic for the UK's Mega Amp Spherical Tokamak (MAST). The diagnostic can image flows of intrinsic C II, C III and He II impurity ions over fields of view between 10 - 45 degrees, at frame rates between 50Hz - 1kHz and with flow resolution typically around 1km/s (compared with measured flows of typically 5 - 30km/s). Spatial resolution is better than ~4.5 cm over a 1.4 x 1.4m area of the plasma cross-section. After reviewing the principles and theory of the coherence imaging technique, the design of a coherence imaging flow diagnostic for MAST is presented in detail. Results of careful laboratory characterization and calibration of the instrument are presented, and the instrument performance is compared to the design calculations. The diagnostic was used successfully for flow measurements on MAST during an experimental campaign in May - September 2013. On-plasma validation of the instrument performance is presented, as well as examples of novel flow observations made with the diagnostic. These include field-aligned flow structures associated with high field side gas fuelling of the plasma, and the first measurements of spatial flow structure in the divertor associated with the application of resonant magnetic perturbations (RMPs). Possible future improvements to the instrument design and extensions of the present work are suggested

    Shear flow visualization at high Reynolds Numbers

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    Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering, 1998.Includes bibliographical references (leaves 92-94).The mechanisms responsible for various disturbances in the wakes of ships have been investigated for some time. Efforts to define and characterize the contributing factors and resulting turbulent wake manifestations conclude that ship length, speed and geometry play integral and interdependent roles. Previous experimentation in the Ocean Engineering Towing Tank at MIT on small scale model ships supplied data for Reynold's Numbers up to ~ 0(106). The work included in this thesis represents a continuation of those efforts up to Re O(107) using a model DDG51 (5514) Destroyer. Through endeavors to identify wake phenomena and closely examine possible sources, previously unvisualized charicteristics were revealed and the calibration, comparison and validation of numerical simulations were made possible. Experimental efforts were concentrated on the study of flow in the wake and near the bow of the model DDG-51 Destroyer (5514). Qualitative and quantitative flow visualization methods were adapted, designed and implemented including ship-fixed and tank fixed streak videography and Digital Particle Image Velocimetry (DPIV). In addition, the experimental apparatus was modified for similar flow visualization near live fish, and a description of this endeavor and its progress are included.by Danielle Ames.S.M

    A novel compact Shearographic NDT system

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    Includes bibliographical referencesThere is a need in industry and the NDT (Non-destructive Testing) community for quick, reliable, user-friendly and cost-effective compact NDT systems that can be used on a wide variety of materials and structures, for quality assurance and maintenance. Designing and building a compact Shearographic NDT system will enhance the capability of inspection during quality assurance and maintenance routines as well as reduce inspection time. Older compact Shearographic systems, which have been tested satisfactorily both under laboratory and field conditions at the NDT Laboratory at the University of Cape Town, have a rather restricted field of view. This is due to the proprietary shearing optics being placed in front of the camera lens, which in other words means that the field of view can only be increased by using a relatively small focal length camera lens which results in having to increase the size of the shearing optics. This would make the compact Shearographic device much larger which is counter-productive since technology enables/directs research and development toward more compact devices

    Extended dynamic range from a combined linear-logarithmic CMOS image sensor

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    Fusion of LIDAR with stereo camera data - an assessment

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    This thesis explores data fusion of LIDAR (laser range-finding) with stereo matching, with a particular emphasis on close-range industrial 3D imaging. Recently there has been interest in improving the robustness of stereo matching using data fusion with active range data. These range data have typically been acquired using time of flight cameras (ToFCs), however ToFCs offer poor spatial resolution and are noisy. Comparatively little work has been performed using LIDAR. It is argued that stereo and LIDAR are complementary and there are numerous advantages to integrating LIDAR into stereo systems. For instance, camera calibration is a necessary prerequisite for stereo 3D reconstruction, but the process is often tedious and requires precise calibration targets. It is shown that a visible-beam LIDAR enables automatic, accurate (sub-pixel) extrinsic and intrinsic camera calibration without any explicit targets. Two methods for using LIDAR to assist dense disparity maps from featureless scenes were investigated. The first involved using a LIDAR to provide high-confidence seed points for a region growing stereo matching algorithm. It is shown that these seed points allow dense matching in scenes which fail to match using stereo alone. Secondly, LIDAR was used to provide artificial texture in featureless image regions. Texture was generated by combining real or simulated images of every point the laser hits to form a pseudo-random pattern. Machine learning was used to determine the image regions that are most likely to be stereo- matched, reducing the number of LIDAR points required. Results are compared to competing techniques such as laser speckle, data projection and diffractive optical elements
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