The Experts below are selected from a list of 294 Experts worldwide ranked by ideXlab platform
Xu Liu - One of the best experts on this subject based on the ideXlab platform.
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Chip-based wide-field 3D nanoscopy through tunable spatial-frequency-Shift Effect
Advanced Optical Imaging Technologies III, 2020Co-Authors: Tang Mingwei, Xiaowei Liu, Qing Yang, Xu LiuAbstract:Linear super-resolution microscopy via synthesis aperture approach permits fast acquisition owing to its wide-field implementations. However, it has been limited in resolution because a spatial-frequency band missing occurs when trying to use a Shift magnitude surpassing the cutoff frequency of the detection system beyond a factor of two, which distorts the image severely. Here, we propose a method of chip-based 3D nanoscopy through a tunable spatial-frequency-Shift Effect capable of covering the full extent of the spatial-frequency component within a wide passband. The missing of the spatial spectrum can be Effectively solved by developing a spatial-frequency-Shift active tuning approach through wave vector manipulation and operation of optical modes propagating along multiple azimuthal directions on a waveguide chip. Besides, the method includes a chip-based sectioning capability, which is enabled by the saturated absorption of fluorophores.
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Wide-field 3D nanoscopy on chip through large and tunable spatial-frequency-Shift Effect
arXiv: Optics, 2019Co-Authors: Xiaowei Liu, Tang Mingwei, Xu Liu, Chao Meng, Xu Xuechu, Chenlei Pang, Yaocheng Shi, Yang Qing, Clemens F. KaminskiAbstract:Linear super-resolution microscopy via synthesis aperture approach permits fast acquisition because of its wide-field implementations, however, it has been limited in resolution because a missing spatial-frequency band occurs when trying to use a Shift magnitude surpassing the cutoff frequency of the detection system beyond a factor of two, which causes ghosting to appear. Here, we propose a method of chip-based 3D nanoscopy through large and tunable spatial-frequency-Shift Effect, capable of covering full extent of the spatial-frequency component within a wide passband. The missing of spatial-frequency can be Effectively solved by developing a spatial-frequency-Shift actively tuning approach through wave vector manipulation and operation of optical modes propagating along multiple azimuthal directions on a waveguide chip to interfere. In addition, the method includes a chip-based sectioning capability, which is enabled by saturated absorption of fluorophores. By introducing ultra-large propagation Effective refractive index, nanoscale resolution is possible, without sacrificing the temporal resolution and the field-of-view. Imaging on GaP waveguide material demonstrates a lateral resolution of lamda/10, which is 5.4 folds above Abbe diffraction limit, and an axial resolution of lamda/19 using 0.9 NA detection objective. Simulation with an assumed propagation Effective refractive index of 10 demonstrates a lateral resolution of lamda/22, in which the huge gap between the directly Shifted and the zero-order components is completely filled to ensure the deep-subwavelength resolvability. It means that, a fast wide-field 3D deep-subdiffraction visualization could be realized using a standard microscope by adding a mass-producible and cost-Effective spatial-frequency-Shift illumination chip.
Y Y Kovalev - One of the best experts on this subject based on the ideXlab platform.
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a bias in vlbi measurements of the core Shift Effect in agn jets
Monthly Notices of the Royal Astronomical Society, 2020Co-Authors: I N Pashchenko, A. M. Kutkin, Y Y Kovalev, A V PlavinAbstract:The Blandford and Konigl model of AGN jets predicts that the position of the apparent opaque jet base - the core - changes with frequency. This Effect is observed with radio interferometry and is widely used to infer parameters and structure of the innermost jet regions. The position of the radio core is typically estimated by fitting a Gaussian template to the interferometric visibilities. This results in a model approximation error, i.e. a bias that can be detected and evaluated through simulations of observations with a realistic jet model. To assess the bias, we construct an artificial sample of sources based on the AGN jet model evaluated on a grid of the parameters derived from a real VLBI flux-density-limited sample and create simulated VLBI data sets at 2.3, 8.1 and 15.4 GHz. We found that the core position Shifts from the true jet apex are generally overestimated. The bias is typically comparable to the core Shift random error and can reach a factor of two for jets with large apparent opening angles. This observational bias depends mostly on the ratio between the true core Shift and the image resolution. This implies that the magnetic field, the core radial distance and the jet speed inferred from the core Shift measurements are overestimated. We present a method to account for the bias.
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a vlba survey of the core Shift Effect in agn jets i evidence of dominating synchrotron opacity
Astronomy and Astrophysics, 2011Co-Authors: Y Y Kovalev, K V Sokolovsky, A Pushkarev, A. P. LobanovAbstract:The Effect of a frequency dependent Shift of the VLBI core position (known as the "core Shift") was predicted more than three decades ago and has since been observed in a few sources, but often within a narrow frequency range. This Effect has important astrophysical and astrometric applications. To achieve a broader understanding of the core Shift Effect and the physics behind it, we conducted a dedicated survey with NRAO's Very Long Baseline Array (VLBA). We used the VLBA to image 20 pre-selected sources simultaneously at nine frequencies in the 1.4-15.4 GHz range. The core position at each frequency was measured by referencing it to a bright, optically thin feature in the jet. A significant core Shift has been successfully measured in each of the twenty sources observed. The median value of the core Shift is found to be 1.21 mas if measured between 1.4 and 15.4 GHz, and 0.24 mas between 5.0 and 15.4 GHz. The core position, r, as a function of frequency, n, is found to be consistent with an r n^-1 law. This behavior is predicted by the Blandford & Koenigl model of a purely synchrotron self-absorbed conical jet in equipartition. No systematic deviation from unity of the power law index in the r(n) relation has been convincingly detected. We conclude that neither free-free absorption nor gradients in pressure and/or density in the jet itself and in the ambient medium surrounding the jet play a significant role in the sources observed within the 1.4-15.4 GHz frequency range. These results support the interpretation of the parsec-scale core as a continuous Blandford-Koenigl type jet with smooth gradients of physical properties along it.
A. P. Lobanov - One of the best experts on this subject based on the ideXlab platform.
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The core Shift Effect in the blazar 3C 454.3
Monthly Notices of the Royal Astronomical Society, 2013Co-Authors: A. M. Kutkin, Margo F. Aller, Kirill Sokolovsky, M. M. Lisakov, Yuri Y. Kovalev, Tuomas Savolainen, P. A. Voytsik, A. P. Lobanov, H. D. Aller, Anne LähteenmäkiAbstract:Opacity-driven Shifts of the apparent VLBI core position with frequency (the "core Shift" Effect) probe physical conditions in the innermost parts of jets in active galactic nuclei. We present the first detailed investigation of this Effect in the brightest gamma-ray blazar 3C454.3 using direct measurements from simultaneous 4.6-43 GHz VLBA observations, and a time lag analysis of 4.8-37 GHz lightcurves from the UMRAO, CrAO, and Metsahovi observations in 2007-2009. The results support the standard Konigl model of jet physics in the VLBI core region. The distance of the core from the jet origin r_c(nu), the core size W(nu), and the lightcurve time lag DT(nu) all depend on the observing frequency nu as r_c(nu)~W(nu)~ DT(nu)~nu^-1/k. The obtained range of k=0.6-0.8 is consistent with the synchrotron self-absorption being the dominating opacity mechanism in the jet. The similar frequency dependence of r_c(nu) and W(nu) suggests that the external pressure gradient does not dictate the jet geometry in the cm-band core region. Assuming equipartition, the magnetic field strength scales with distance r as B = 0.4(r/1pc)^-0.8 G. The total kinetic power of electron/positron jet is about 10^44 ergs/s.
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a vlba survey of the core Shift Effect in agn jets i evidence of dominating synchrotron opacity
Astronomy and Astrophysics, 2011Co-Authors: Y Y Kovalev, K V Sokolovsky, A Pushkarev, A. P. LobanovAbstract:The Effect of a frequency dependent Shift of the VLBI core position (known as the "core Shift") was predicted more than three decades ago and has since been observed in a few sources, but often within a narrow frequency range. This Effect has important astrophysical and astrometric applications. To achieve a broader understanding of the core Shift Effect and the physics behind it, we conducted a dedicated survey with NRAO's Very Long Baseline Array (VLBA). We used the VLBA to image 20 pre-selected sources simultaneously at nine frequencies in the 1.4-15.4 GHz range. The core position at each frequency was measured by referencing it to a bright, optically thin feature in the jet. A significant core Shift has been successfully measured in each of the twenty sources observed. The median value of the core Shift is found to be 1.21 mas if measured between 1.4 and 15.4 GHz, and 0.24 mas between 5.0 and 15.4 GHz. The core position, r, as a function of frequency, n, is found to be consistent with an r n^-1 law. This behavior is predicted by the Blandford & Koenigl model of a purely synchrotron self-absorbed conical jet in equipartition. No systematic deviation from unity of the power law index in the r(n) relation has been convincingly detected. We conclude that neither free-free absorption nor gradients in pressure and/or density in the jet itself and in the ambient medium surrounding the jet play a significant role in the sources observed within the 1.4-15.4 GHz frequency range. These results support the interpretation of the parsec-scale core as a continuous Blandford-Koenigl type jet with smooth gradients of physical properties along it.
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A VLBA survey of the core Shift Effect in AGN jets I. Evidence for dominating synchrotron opacity
Astronomy & Astrophysics, 2011Co-Authors: Kirill Sokolovsky, Yuri Y. Kovalev, A Pushkarev, A. P. LobanovAbstract:The Effect of a frequency dependent Shift of the VLBI core position (known as the "core Shift") was predicted more than three decades ago and has since been observed in a few sources, but often within a narrow frequency range. This Effect has important astrophysical and astrometric applications. To achieve a broader understanding of the core Shift Effect and the physics behind it, we conducted a dedicated survey with NRAO's Very Long Baseline Array (VLBA). We used the VLBA to image 20 pre-selected sources simultaneously at nine frequencies in the 1.4-15.4 GHz range. The core position at each frequency was measured by referencing it to a bright, optically thin feature in the jet. A significant core Shift has been successfully measured in each of the twenty sources observed. The median value of the core Shift is found to be 1.21 mas if measured between 1.4 and 15.4 GHz, and 0.24 mas between 5.0 and 15.4 GHz. The core position, r, as a function of frequency, n, is found to be consistent with an r n^-1 law. This behavior is predicted by the Blandford & Koenigl model of a purely synchrotron self-absorbed conical jet in equipartition. No systematic deviation from unity of the power law index in the r(n) relation has been convincingly detected. We conclude that neither free-free absorption nor gradients in pressure and/or density in the jet itself and in the ambient medium surrounding the jet play a significant role in the sources observed within the 1.4-15.4 GHz frequency range. These results support the interpretation of the parsec-scale core as a continuous Blandford-Koenigl type jet with smooth gradients of physical properties along it.
Tang Mingwei - One of the best experts on this subject based on the ideXlab platform.
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Chip-based wide-field 3D nanoscopy through tunable spatial-frequency-Shift Effect
Advanced Optical Imaging Technologies III, 2020Co-Authors: Tang Mingwei, Xiaowei Liu, Qing Yang, Xu LiuAbstract:Linear super-resolution microscopy via synthesis aperture approach permits fast acquisition owing to its wide-field implementations. However, it has been limited in resolution because a spatial-frequency band missing occurs when trying to use a Shift magnitude surpassing the cutoff frequency of the detection system beyond a factor of two, which distorts the image severely. Here, we propose a method of chip-based 3D nanoscopy through a tunable spatial-frequency-Shift Effect capable of covering the full extent of the spatial-frequency component within a wide passband. The missing of the spatial spectrum can be Effectively solved by developing a spatial-frequency-Shift active tuning approach through wave vector manipulation and operation of optical modes propagating along multiple azimuthal directions on a waveguide chip. Besides, the method includes a chip-based sectioning capability, which is enabled by the saturated absorption of fluorophores.
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Wide-field 3D nanoscopy on chip through large and tunable spatial-frequency-Shift Effect
arXiv: Optics, 2019Co-Authors: Xiaowei Liu, Tang Mingwei, Xu Liu, Chao Meng, Xu Xuechu, Chenlei Pang, Yaocheng Shi, Yang Qing, Clemens F. KaminskiAbstract:Linear super-resolution microscopy via synthesis aperture approach permits fast acquisition because of its wide-field implementations, however, it has been limited in resolution because a missing spatial-frequency band occurs when trying to use a Shift magnitude surpassing the cutoff frequency of the detection system beyond a factor of two, which causes ghosting to appear. Here, we propose a method of chip-based 3D nanoscopy through large and tunable spatial-frequency-Shift Effect, capable of covering full extent of the spatial-frequency component within a wide passband. The missing of spatial-frequency can be Effectively solved by developing a spatial-frequency-Shift actively tuning approach through wave vector manipulation and operation of optical modes propagating along multiple azimuthal directions on a waveguide chip to interfere. In addition, the method includes a chip-based sectioning capability, which is enabled by saturated absorption of fluorophores. By introducing ultra-large propagation Effective refractive index, nanoscale resolution is possible, without sacrificing the temporal resolution and the field-of-view. Imaging on GaP waveguide material demonstrates a lateral resolution of lamda/10, which is 5.4 folds above Abbe diffraction limit, and an axial resolution of lamda/19 using 0.9 NA detection objective. Simulation with an assumed propagation Effective refractive index of 10 demonstrates a lateral resolution of lamda/22, in which the huge gap between the directly Shifted and the zero-order components is completely filled to ensure the deep-subwavelength resolvability. It means that, a fast wide-field 3D deep-subdiffraction visualization could be realized using a standard microscope by adding a mass-producible and cost-Effective spatial-frequency-Shift illumination chip.
Xiaowei Liu - One of the best experts on this subject based on the ideXlab platform.
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Chip-based wide-field 3D nanoscopy through tunable spatial-frequency-Shift Effect
Advanced Optical Imaging Technologies III, 2020Co-Authors: Tang Mingwei, Xiaowei Liu, Qing Yang, Xu LiuAbstract:Linear super-resolution microscopy via synthesis aperture approach permits fast acquisition owing to its wide-field implementations. However, it has been limited in resolution because a spatial-frequency band missing occurs when trying to use a Shift magnitude surpassing the cutoff frequency of the detection system beyond a factor of two, which distorts the image severely. Here, we propose a method of chip-based 3D nanoscopy through a tunable spatial-frequency-Shift Effect capable of covering the full extent of the spatial-frequency component within a wide passband. The missing of the spatial spectrum can be Effectively solved by developing a spatial-frequency-Shift active tuning approach through wave vector manipulation and operation of optical modes propagating along multiple azimuthal directions on a waveguide chip. Besides, the method includes a chip-based sectioning capability, which is enabled by the saturated absorption of fluorophores.
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Wide-field 3D nanoscopy on chip through large and tunable spatial-frequency-Shift Effect
arXiv: Optics, 2019Co-Authors: Xiaowei Liu, Tang Mingwei, Xu Liu, Chao Meng, Xu Xuechu, Chenlei Pang, Yaocheng Shi, Yang Qing, Clemens F. KaminskiAbstract:Linear super-resolution microscopy via synthesis aperture approach permits fast acquisition because of its wide-field implementations, however, it has been limited in resolution because a missing spatial-frequency band occurs when trying to use a Shift magnitude surpassing the cutoff frequency of the detection system beyond a factor of two, which causes ghosting to appear. Here, we propose a method of chip-based 3D nanoscopy through large and tunable spatial-frequency-Shift Effect, capable of covering full extent of the spatial-frequency component within a wide passband. The missing of spatial-frequency can be Effectively solved by developing a spatial-frequency-Shift actively tuning approach through wave vector manipulation and operation of optical modes propagating along multiple azimuthal directions on a waveguide chip to interfere. In addition, the method includes a chip-based sectioning capability, which is enabled by saturated absorption of fluorophores. By introducing ultra-large propagation Effective refractive index, nanoscale resolution is possible, without sacrificing the temporal resolution and the field-of-view. Imaging on GaP waveguide material demonstrates a lateral resolution of lamda/10, which is 5.4 folds above Abbe diffraction limit, and an axial resolution of lamda/19 using 0.9 NA detection objective. Simulation with an assumed propagation Effective refractive index of 10 demonstrates a lateral resolution of lamda/22, in which the huge gap between the directly Shifted and the zero-order components is completely filled to ensure the deep-subwavelength resolvability. It means that, a fast wide-field 3D deep-subdiffraction visualization could be realized using a standard microscope by adding a mass-producible and cost-Effective spatial-frequency-Shift illumination chip.
