Topic
Speckle imaging
About: Speckle imaging is a research topic. Over the lifetime, 3730 publications have been published within this topic receiving 62354 citations.
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TL;DR: A two-dimensional high angular resolution study of Mira (Mira) was carried out at four epochs from 1983 November to 1988 November using speckle interferometry techniques, which detected asymmetries in the extended atmosphere of this pulsating star as mentioned in this paper.
Abstract: A two-dimensional high angular resolution study of ο Ceti (Mira), carried out at four epochs from 1983 November to 1988 November using speckle interferometry techniques, detected asymmetries in the extended atmosphere of this pulsating star The reconstructed speckle images show that the strength and the shape of this asymmetry changes as a function of wavelength and time The position angles of the major axes of the asymmetries at different epochs are determined and the axes are measured accurately as a function of wavelength The origin of the observed asymmetries has not yet been identified Plausible causes include instabilities in the pulsating atmosphere, nonspherical pulsation, or the interaction with the nearby companion
50 citations
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TL;DR: In this paper, the authors report observations from its successor GI2T, which show further high-resolution details of the hydrogen envelope, which clearly show the envelope in rotation and approximately fit a disk model.
Abstract: CERTAIN hot stars, belonging to the Be class, may have an envelope of hydrogen gas, possibly in the form of a rotating disk1 or spheroidal shell2. Other models involve elliptical rings3 or close binary systems where the Roche lobe of the companion is filled with hydrogen2. The angular size of these features is too small for direct detection by conventional telescopes, and attempts to resolve the structure using speckle interferometry (a technique that restores the diffraction-limited resolution otherwise degraded or spoiled by the atmosphere) have failed. The various models of the structure of the hydrogen envelope are based on spectroscopic data, together with polarization and variability measurements. After a century of spectroscopic observations, which showed considerable but little-understood variations, the hydrogen envelope of the star gamma Cassiopeiae was angularly resolved by the prototype interferometer I2T in 1986 (ref. 4). Here we report observations from its successor GI2T, which show further high-resolution details of the hydrogen envelope. The data clearly show the envelope in rotation and approximately fit a disk model. Thus, the GI2T yields optical information capable of constraining astrophysical models on a milliarcsecond scale.
50 citations
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TL;DR: Results show that, using an imaging frame rate of 2000 frames per second, CESI can effectively render flow acceleration and deceleration with visual continuity and is effective in depicting how stenosis-related flow disturbance events, such as flow jet formation and post-stenotic flow recirculation, evolve spatiotemporally over a pulse cycle.
Abstract: Realization of flow imaging at high frame rates is essential to the visualization of complex flow patterns with fast-changing spatiotemporal dynamics. In this study, we present an experimental demonstration of a novel ultrasound-based high-frame-rate flow visualization technique called color-encoded speckle imaging (CESI), which depicts flow information in a hybrid form comprising flow speckle pattern and color-encoded velocity mapping. This technique works by integrating two key principles: (i) using broad-view data acquisition schemes like plane wave compounding to obtain image data at frame rates well beyond the video display range and (ii) deriving and displaying both flow speckles and velocity estimates from the acquired broad-view image data. CESI was realized on a channel-domain ultrasound imaging research platform, and its performance was evaluated in the context of monitoring complex flow dynamics inside a carotid bifurcation flow phantom with 25% eccentric stenosis at the inlet of the internal carotid artery. Results show that, using an imaging frame rate of 2000 frames per second (based on plane wave compounding with five steering angles), CESI can effectively render flow acceleration and deceleration with visual continuity. It is also effective in depicting how stenosis-related flow disturbance events, such as flow jet formation and post-stenotic flow recirculation, evolve spatiotemporally over a pulse cycle. We anticipate that CESI can represent a rational approach to rendering flow information in ultrasound-based vascular diagnoses.
50 citations
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TL;DR: This work describes an original acousto-optic method that allows one to reveal optical contrasts through biological tissues that are several centimeters thick with a millimeter-sized resolution and improves the observed degree of modulation by 2 orders of magnitude.
Abstract: An original acousto-optic method is described that allows one to reveal optical contrasts through biological tissues that are several centimeters thick with a millimeter-sized resolution. This technique is based on the interaction of scattered laser light with a focused ultrasonic field. The modulation depth of the optical speckle is related to local optical properties of the sample. Our parallel-processing approach to the demodulation of the speckle improves the observed degree of modulation by 2 orders of magnitude and quickly yields a good statistical value. Optically absorbing objects were imaged inside 35-mm-thick biological tissues.
50 citations
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TL;DR: The results of speckle runs at the 4.1m Southern Astronomical Research (SOAR) telescope in 2012 and 2013 were reported in this paper, where a total of 586 objects were observed.
Abstract: We report the results of speckle runs at the 4.1-m Southern Astronomical Research (SOAR) telescope in 2012 and 2013. A total of 586 objects were observed. We give 699 measurements of 487 resolved binaries and upper detection limits for 112 unresolved stars. Eleven pairs (including one triple) were resolved for the first time. Orbital elements have been determined for the first time for 13 pairs; orbits of another 45 binaries are revised or updated.
50 citations