Tomographic Signal Research Articles

H-alpha and Ca ii Infrared Triplet Variations During a Transit of the 23 Myr Planet V1298 Tau c

Abstract Young transiting exoplanets (<100 Myr) provide crucial insight into atmospheric evolution via photoevaporation. However, transmission spectroscopy measurements to determine atmospheric composition and mass loss are challenging due to the activity and prominent stellar disk inhomogeneities present on young stars. We observed a full transit of V1298 Tau c, a 23 Myr, 5.59 R ⊕ planet orbiting a young K0-K1.5 solar analog with GRACES on Gemini North. We were able to measure the Doppler tomographic signal of V1298 Tau c using the Ca ii infrared triplet (IRT) and find a projected obliquity of λ = 5° ± 15°. The tomographic signal is only seen in the chromospherically driven core of the Ca ii IRT, which may be the result of star-planet interactions. Additionally, we find that excess absorption of the Hα line decreases smoothly during the transit. While this could be a tentative detection of hot gas escaping the planet, we find this variation is consistent with similar timescale observations of other young stars that lack transiting planets over similar timescales. We show this variation can also be explained by the presence of starspots with surrounding facular regions. More observations both in and out of the transits of V1298 Tau c are required to determine the nature of the Ca ii IRT and Hα line variations.

Thermal Drifts of Capacitive Flow Meters: Analysis of Effects and Model-Based Compensation

Capacitive sensing has become a favorable measurement technology for flow metering in pneumatic conveying systems. Multielectrode sensing structures and tomographic signal evaluations enable spatially resolved flow parameter estimation, which is of particular interest for pneumatically conveyed solids due to inhomogeneous particle distributions within the pipeline. The noninvasive working principle of capacitive sensors is an important feature for the application in industrial processes with harsh environments. However, cross sensitivities of the capacitive probe cause effects, such as temperature drifts of the measurements. For a reliable operation of capacitive flow meters in harsh environments, induced drifts have to be compensated. In this article, we present the detailed analyses of thermal effects within capacitive sensors. Based on the findings, a model-based temperature compensation approach is developed within the Bayesian framework. The performance of the proposed compensation approach is analyzed by a measurement-based validation within a climate chamber and by a simulation-based uncertainty quantification. The capability to obtain temperature-independent estimates with calibration measurements acquired at room temperature is demonstrated.

On the Slow-Time k-Space and its Augmentation in Doppler Radar Tomography.

Doppler Radar Tomography (DRT) relies on spatial diversity from rotational motion of a target rather than spectral diversity from wide bandwidth signals. The slow-time k-space is a novel form of the spatial frequency space generated by the relative rotational motion of a target at a single radar frequency, which can be exploited for high-resolution target imaging by a narrowband radar with Doppler tomographic signal processing. This paper builds on a previously published work and demonstrates, with real experimental data, a unique and interesting characteristic of the slow-time k-space: it can be augmented and significantly enhance imaging resolution by signal processing. High resolution can reveal finer details in the image, providing more information to identify unknown targets detected by the radar.

Deep learning from 21-cm tomography of the Cosmic Dawn and Reionization

The 21-cm power spectrum (PS) has been shown to be a powerful discriminant of reionization and cosmic dawn astrophysical parameters. However, the 21-cm tomographic signal is highly non-Gaussian. Therefore there is additional information which is wasted if only the PS is used for parameter recovery. Here we showcase astrophysical parameter recovery directly from 21-cm images, using deep learning with convolutional neural networks (CNN). Using a database of 2D images taken from 10,000 21-cm lightcones (each generated from different cosmological initial conditions), we show that a CNN is able to recover parameters describing the first galaxies: (i) Tvir , their minimum host halo virial temperatures (or masses) capable of hosting efficient star formation; (ii) {\zeta} , their typical ionizing efficiencies; (iii) LX/SFR , their typical soft-band X-ray luminosity to star formation rate; and (iv) E0 , the minimum X-ray energy capable of escaping the galaxy into the IGM. For most of their allowed ranges, log Tvir and log LX/SFR are recovered with < 1% uncertainty, while {\zeta} and E0 are recovered within 10% uncertainty. Our results are roughly comparable to the accuracy obtained from Monte Carlo Markov Chain sampling of the PS with 21CMMC for the two mock observations analyzed previously, although we caution that we do not yet include noise and foreground contaminants in this proof-of-concept study.

Low-dose x-ray tomography through a deep convolutional neural network

Synchrotron-based X-ray tomography offers the potential for rapid large-scale reconstructions of the interiors of materials and biological tissue at fine resolution. However, for radiation sensitive samples, there remain fundamental trade-offs between damaging samples during longer acquisition times and reducing signals with shorter acquisition times. We present a deep convolutional neural network (CNN) method that increases the acquired X-ray tomographic signal by at least a factor of 10 during low-dose fast acquisition by improving the quality of recorded projections. Short-exposure-time projections enhanced with CNNs show signal-to-noise ratios similar to long-exposure-time projections. They also show lower noise and more structural information than low-dose short-exposure acquisitions post-processed by other techniques. We evaluated this approach using simulated samples and further validated it with experimental data from radiation sensitive mouse brains acquired in a tomographic setting with transmission X-ray microscopy. We demonstrate that automated algorithms can reliably trace brain structures in low-dose datasets enhanced with CNN. This method can be applied to other tomographic or scanning based X-ray imaging techniques and has great potential for studying faster dynamics in specimens

En face 3D‐SDOCT images and the saltmarshes sign

AbstractPurpose To investigate the signal intensity obtained from the vitreoretinal interface using the spectral domain 3D OCT images.Methods Review of spectral domain optical coherence tomography (OCT) examinations; mapping of the intensity of the tomographic signal over the posterior pole using the 3D reconstruction software; Retrospective study of the signs revealed. Chi‐square was used.Results Mapping the signal intensity over the posterior pole was named as Vitreoretinal Interface Signal Topography (V.I.SI.T.); VISIT images offer views of the epicenters and retinal folds associated with epiretinal membranes, a tool to followup the progress of the disease and to investigate the direction of the tractional forces; VISIT images allow the visualization of the borders of internal limiting membrane peeling and the inner retinal defects after an ILM rhexis; VISIT images revealed white plaques at the vitreoretinal interface, which were named as saltmarshes (SAM); SAMs are reproducible, exhibit interocular symmetry, faint in older ages and they correlate with the epicenters of ERMs.Conclusion En face VISIT images offers unique information about the vitreoretinal interface; the saltmarshes sign may indicate the areas of strong vitreoretinal adherence and strain and/or the cortex remnants after a posterior vitreous detachment.

Angular fluctuations in the CXB: is Fe 6.4 keV line tomography of the large-scale structure feasible?

AGN are known to account for a major portion, if not all, of the cosmic X-ray background radiation. The dominant sharp spectral feature in their spectra is the 6.4 keV fluorescent line of iron, which may contribute to as much as ~ 5-10 % of the CXB spectral intensity at ~ 2-6 keV. Owing to cosmological redshift, the line photons detected at the energy E carry information about objects located at the redshift z=6.4/E-1. In particular, imprinted in their angular fluctuations is the information about the large-scale structure at redshift z. This opens the possibility of performing the Fe K_alpha line tomography of the cosmic large-scale structure. We show that detection of the tomographic signal at ~100 sigma confidence requires an all-sky survey by an instrument with an effective area of ~10 m^2 and field of view of ~1 deg^2. The signal is strongest for objects located at the redshift z~1 and at the angular scales corresponding to l ~ 100-300, therefore an optimal detection can be achieved with an instrument having a rather modest angular resolution of ~ 0.1-0.5 deg. For such an instrument, the CCD-type energy resolution of ~ 100-200 eV FWHM is entirely sufficient for the optimal separation of the signals coming from different redshifts. The gain in the signal strength that could potentially be achieved with energy resolution comparable to the line width is nullified by the photon counting and AGN discreteness noise. Among the currently planned and proposed missions, these requirements are best satisfied by LOFT, even though it was proposed for an entirely different purpose. Among others, clear detection should be achieved by WFXT (~ 20-35 sigma) and ATHENA (~ 10-20 sigma). eROSITA, in the course of its 4 years all-sky survey, will detect the tomographic signal only marginally.

Tomographic magnification of Lyman-break galaxies in the Deep Lens Survey

Using about 450,000 galaxies in the Deep Lens Survey, we present a detection of the gravitational magnification of z > 4 Lyman Break Galaxies by massive foreground galaxies with 0.4 < z < 1.0, grouped by redshift. The magnification signal is detected at S/N greater than 20, and rigorous checks confirm that it is not contaminated by any galaxy sample overlap in redshift. The inferred galaxy mass profiles are consistent with earlier lensing analyses at lower redshift. We then explore the tomographic lens magnification signal by splitting our foreground galaxy sample into 7 redshift bins. Combining galaxy-magnification cross-correlations and galaxy angular auto-correlations, we develop a bias-independent estimator of the tomographic signal. As a diagnostic of magnification tomography, the measurement of this estimator rejects a flat dark matter dominated Universe at > 7.5{\sigma} with a fixed \sigma_8 and is found to be consistent with the expected redshift-dependence of the WMAP7 {\Lambda}CDM cosmology.

Multisignal Compressed Sensing for Polarimetric SAR Tomography

In recent years, 3-D imaging by means of polarimetric synthetic aperture radar (SAR) sensors has become a field of intensive research. In SAR tomography, the vertical reflectivity function for every azimuth-range pixel is usually recovered by processing data collected using a defined repeat-pass acquisition geometry. The most common approach is to generate a synthetic aperture in the elevation direction through imaging from a large number of parallel tracks. This imaging technique is appealing, since it is very simple. However, it has the drawback that large temporal baselines can severely affect the reconstruction. In an attempt to reduce the number of parallel tracks, we propose a new approach that exploits structural correlations between neighboring azimuth-range pixels and/or polarimetric channels. As a matter of fact, this can be done under the framework of distributed compressed sensing (CS) (DCS), which stems from CS theory, thus also exploiting sparsity in the tomographic signal. Finally, results demonstrating the potential of the DCS methodology will be validated by using fully polarimetric L-band data acquired by the E-SAR sensor of the German Aerospace Center (DLR).

Optical Coherence Tomography: its role in the non-invasive structural examination and conservation of cultural heritage objects—a review

A brief introduction to Optical Coherence Tomography (OCT) is presented, stressing the origin of the tomographic signal and the detection methods defining various modalities of the technique. The parameters of the tomographs, such as axial and lateral resolution, wavelength and intensity of the probing light, imaging range, time of examination, and sensitivity are then defined, and a paradigm for interpreting the OCT tomograms provided. The second part of the article comprises a review of the utilisation of OCT for structural examination of artworks, illustrated with some representative results. Applications to the structural imaging of semi-transparent subsurface layers such as varnishes and glazes, of underdrawings and of reverse painting on glass, are described first, and then applications in the examination of the structure and state of preservation of historic glass, jade, glazed porcelain and faience are discussed. Finally, the use of OCT combined with LIBS analysis and laser ablation of surface layers is presented.

Ex Vivo Thermoacoustic Imaging Over Large Fields of View With 108 MHz Irradiation

Thermoacoustic signals are generated over a large field of view by 900 ns TE10 pulses with 108 MHz carrier frequency. Test specimens selectively absorb the TE10 pulse energy producing rapid thermal expansions that generate ultrasonic pulses. 108 MHz irradiation provides excellent depth penetration in soft tissue, allowing blood and physiologic saline to generate strong signals. Thermoacoustic signal generation from a depth of several cm is well above our systems noise floor. Rotating the test specimen provides single-slice tomographic signal encoding. Filtered back-projection reconstruction yields images over a 6.4 cm field of view. Reconstructions of tissue mimicking prostate phantoms and fresh porcine kidney tissue are presented.

10/20, 10/10, and 10/5 systems revisited: Their validity as relative head-surface-based positioning systems

With the advent of multi-channel EEG hardware systems and the concurrent development of topographic and tomographic signal source localization methods, the international 10/20 system, a standard system for electrode positioning with 21 electrodes, was extended to higher density electrode settings such as 10/10 and 10/5 systems, allowing more than 300 electrode positions. However, their effectiveness as relative head-surface-based positioning systems has not been examined. We previously developed a virtual 10/20 measurement algorithm that can analyze any structural MR head and brain image. Extending this method to the virtual 10/10 and 10/5 measurement algorithms, we analyzed the MR images of 17 healthy subjects. The acquired scalp positions of the 10/10 and 10/5 systems were normalized to the Montreal Neurological Institute (MNI) stereotactic coordinates and their spatial variability was assessed. We described and examined the effects of spatial variability due to the selection of positioning systems and landmark placement strategies. As long as a detailed rule for a particular system was provided, it yielded precise landmark positions on the scalp. Moreover, we evaluated the effective spatial resolution of 329 scalp landmark positions of the 10/5 system for multi-subject studies. As long as a detailed rule for landmark setting was provided, 241 scalp positions could be set effectively when there was no overlapping of two neighboring positions. Importantly, 10/10 positions could be well separated on a scalp without overlapping. This study presents a referential framework for establishing the effective spatial resolutions of 10/20, 10/10, and 10/5 systems as relative head-surface-based positioning systems.

FLUCTUATIONS OF THE MODAL ARRIVAL TIMES DUE TO LINEAR INTERNAL WAVES: APPLICATION TO INVERSION

It is well known that internal waves in the ocean are an important source of environmental variability which has serious effects in the structure of an acoustic field due to a known source. When measurements of the acoustic field form the input data for an inversion procedure aiming at the recovery of the environmental parameters, the information they carry on includes the internal wave effects. It is therefore natural to assume that neglecting the effects of the internal waves in an inversion procedure based on acoustic field measurements, errors are induced in the inversion. The paper deals with this problem and addresses the case of inversion schemes using travel time information of an acoustic signal. Using a statistical 2D model of the internal waves, based on the Garrett and Munk spectrum, the spatial and temporal evolution of the internal waves field as well as the fluctuations of the sound speed profile is estimated for a characteristic shallow-water environment. Considering a sound speed anomaly in the water column as the oceanographic feature to be recovered, the paper studies the influence of the internal waves field on the modal travel time information obtained through the propagation of a tomographic signal through this environment. The sound speed anomaly denoted as "current" is described by a suitable Gaussian function. Using an analytical expression based on a perturbation approach, the difference in the modal arrival times calculated for a background environment and a perturbed one (considering that the sound speed perturbations are due either to a current or to the summation of a current and of the internal waves field) was calculated for each propagating mode of the waveguide. These calculations led to the conclusion that the internal waves have a non-negligible impact on the arrival times and that the maximum amplitude of a current can be under- or overestimated of several meters per second when these waves are not taken into account in the inversion method, whereas they are present in the oceanic medium.

Seismic heterogeneity in the mantle—strong shear wave signature of slabs from joint tomography

The primary source of information on heterogeneity within the Earth comes from seismic tomography. A powerful tool for examining the character of heterogeneity comes from the comparison of images of bulk-sound and shear wavespeed extracted in a single inversion, since this isolates the dependencies on the elastic moduli. However, particularly in such multi-parameter inversions there are many hidden facets which can have a strong influence on the results, such as the weightings between parameters and in the misfit functions. Joint inversion with restricted data sets giving comparable cover for P and S waves provides useful checks on more inclusive studies, and can provide relatively high resolution in some areas. The relative behaviour of bulk-sound and shear wavespeed can provide a useful guide to the definition of heterogeneity regimes. For subduction zones a large part of the tomographic signal comes from S wavespeed variations. In the upper mantle and transition there can be significant bulk-sound speed contributions for younger slabs, and in stagnant slabs associated with slab roll-back. For subducted oceanic lithosphere older than about 90 Ma shear wavespeed variations nearly always are dominant and so the P wave images are controlled by shear modulus variations. The narrow segments of fast wavespeeds in the depth range 900–1500 km in the lower mantle are dominated by S variations, with very little bulk-sound contribution. Deep in the mantle there are many fast features without obvious association with subduction in the last 100 Ma, which suggests long-lived preservation of components of the geodynamic cycle.

In-Line Monitoring of Rheological Parameters with an Electromagnetic Flowmeter

Tomographic signal processing has been added to a conventional electromagnetic flowmeter. The result is a new method for measuring rheological parameters of viscous, non-Newtonian fluids. The practical realization requires only minor changes to existing instruments. Hence their main advantages are maintained, such as non-invasive, in-line measurement without pressure drop. The basic idea is to generate two different magnetic fields with the flowmeter by switching the current direction in one of the magnetic coils. The flowmeter measures two signals depending on the flow profile. Using simple parametric models for both the flow profile and the rheology, the flow profile can be calculated from the flowmeter signals, and from the flow profile the rheological behaviour is determined. The theory and experimental results with a slightly modified industrial flowmeter are presented.

Sensing three-dimensional index-of-refraction variations by means of optical wavefront sensor measurements and tomographic reconstruction

Light waves propagating through a region of inhomogeneous index of refraction are aberrated. Turbulent air flows cause such inhomogeneities to arise from density fluctuations within the flow, which affect the index of refraction of air. Here we describe a technique for measuring the 3-D structure of the index-of-refraction distribution in a turbulent air flow using optical wavefront sensor measurements and tomographic signal reconstruction. Use of wavefront sensor measurements offers higherspeed measurement than previously used holographic methods, while providing high-fidelity reconstructions. We discuss Hartmann sensor measurements and wavefront reconstruction. Sampling requirements are also addressed, including the effects of a limited number of projections and wavefront subaperture size. Theory, simulation, and experimental results are presented.

Dynamic stereo imaging of hard-skinned sonar targets

The visible portion of a hard-skinned sonar target can be scanned in xyz coordinates by beamforming a planar array, to give a 3-D representation. However, a simple line array running along the x axis can provide a projection view of a target that lies along the z axis, with its upper and lower surfaces being projected semitransparently onto the xz plane, giving a picture analogous to that of a biological specimen viewed with a slide microscope. If the line array is tumbled about the z axis, it will appear that the target is revolving around the z axis. When this tumbling view is presented 14° out of phase to the left and right eyes, a stereoscopic view of the tumbling target is obtained, with its 3-D form revealed by the brain’s innate tomographic signal processing capability. In-water experiments have been conducted for several target shapes. Other means of generating dynamic displays have been developed that are suitable for scanning objects on the seafloor. A videotape of results for several targets has been prepared. Further simplifications of the array structure and processing are possible, with some limitations and weaknesses. [Work supported by ARL:UT IR&amp;D.]

Revolving-projection stereo imaging of hard-skinned sonar targets

It is well known that the three-dimensional shell geometry of the visible portion of a distant hard-skinned sonar target can be scanned in xy coordinates by beamforming a planar array, with the associated z coordinates being provided by time gating the acoustic return. However, a simple line array running along the x axis can provide a projection view of the target, with its upper and lower surfaces being projected semi-transparently onto the xz plane, giving a picture analogous to that of a paramecium viewed with a slide microscope. If the line array is now tumbled in the xy plane, it will appear that the target is revolving around the z axis. When this tumbling view is presented 14° out of phase to the left and right eyes, a stereoscopic view of the tumbling target is obtained, thus revealing its three-dimensional form (with the aid of the brain’s innate tomographic signal processing powers). Further simplifications of the array structure and processing are possible, with some limitations and weaknesses. A videotape of results for several targets has been prepared for presentation.

Lesions that manifest as medial cheek and nasolabial fold masses.

Seventeen cases were collected in which the patient presented with a medial cheek or nasolabial fold mass. Most of these lesions were uncommon, and some were rare. The most reliable differentiating finding was the type of associated bone involvement. The malignancies had bone erosion and as a group could be distinguished from the other masses. Computed tomographic attenuation and magnetic resonance imaging signal intensities were nonspecific and did not allow a definitive diagnosis to be made. The types of pathologic conditions and their sectional imaging findings are reviewed.

Ultrasound hyperthermia apparatus

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