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  • 1
    Online Resource
    Online Resource
    First Sagittarius A* Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole in the Center of the Milky Way
    American Astronomical Society ; 2022
    In:  The Astrophysical Journal Letters Vol. 930, No. 2 ( 2022-05-01), p. L12-
    Details
    In: The Astrophysical Journal Letters, American Astronomical Society, Vol. 930, No. 2 ( 2022-05-01), p. L12-
    Abstract: We present the first Event Horizon Telescope (EHT) observations of Sagittarius A* (Sgr A*), the Galactic center source associated with a supermassive black hole. These observations were conducted in 2017 using a global interferometric array of eight telescopes operating at a wavelength of λ = 1.3 mm. The EHT data resolve a compact emission region with intrahour variability. A variety of imaging and modeling analyses all support an image that is dominated by a bright, thick ring with a diameter of 51.8 ± 2.3 μ as (68% credible interval). The ring has modest azimuthal brightness asymmetry and a comparatively dim interior. Using a large suite of numerical simulations, we demonstrate that the EHT images of Sgr A* are consistent with the expected appearance of a Kerr black hole with mass ∼4 × 10 6 M ⊙ , which is inferred to exist at this location based on previous infrared observations of individual stellar orbits, as well as maser proper-motion studies. Our model comparisons disfavor scenarios where the black hole is viewed at high inclination ( i 〉 50°), as well as nonspinning black holes and those with retrograde accretion disks. Our results provide direct evidence for the presence of a supermassive black hole at the center of the Milky Way, and for the first time we connect the predictions from dynamical measurements of stellar orbits on scales of 10 3 –10 5 gravitational radii to event-horizon-scale images and variability. Furthermore, a comparison with the EHT results for the supermassive black hole M87* shows consistency with the predictions of general relativity spanning over three orders of magnitude in central mass.
    Type of Medium: Online Resource
    ISSN: 2041-8205 , 2041-8213
    URL: Article
    DOI: 10.3847/2041-8213/ac6674
    Language: Unknown
    Publisher: American Astronomical Society
    Publication Date: 2022
    detail.hit.zdb_id: 7233-3
    detail.hit.zdb_id: 2006858-X
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  • 2
    Online Resource
    Online Resource
    First M87 Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole
    American Astronomical Society ; 2019
    In:  The Astrophysical Journal Letters Vol. 875, No. 1 ( 2019-04-10), p. L1-
    Details
    In: The Astrophysical Journal Letters, American Astronomical Society, Vol. 875, No. 1 ( 2019-04-10), p. L1-
    Abstract: When surrounded by a transparent emission region, black holes are expected to reveal a dark shadow caused by gravitational light bending and photon capture at the event horizon. To image and study this phenomenon, we have assembled the Event Horizon Telescope, a global very long baseline interferometry array observing at a wavelength of 1.3 mm. This allows us to reconstruct event-horizon-scale images of the supermassive black hole candidate in the center of the giant elliptical galaxy M87. We have resolved the central compact radio source as an asymmetric bright emission ring with a diameter of 42 ± 3 μ as, which is circular and encompasses a central depression in brightness with a flux ratio ≳10:1. The emission ring is recovered using different calibration and imaging schemes, with its diameter and width remaining stable over four different observations carried out in different days. Overall, the observed image is consistent with expectations for the shadow of a Kerr black hole as predicted by general relativity. The asymmetry in brightness in the ring can be explained in terms of relativistic beaming of the emission from a plasma rotating close to the speed of light around a black hole. We compare our images to an extensive library of ray-traced general-relativistic magnetohydrodynamic simulations of black holes and derive a central mass of M  = (6.5 ± 0.7) × 10 9 M ⊙ . Our radio-wave observations thus provide powerful evidence for the presence of supermassive black holes in centers of galaxies and as the central engines of active galactic nuclei. They also present a new tool to explore gravity in its most extreme limit and on a mass scale that was so far not accessible.
    Type of Medium: Online Resource
    ISSN: 2041-8205 , 2041-8213
    URL: Article
    DOI: 10.3847/2041-8213/ab0ec7
    Language: Unknown
    Publisher: American Astronomical Society
    Publication Date: 2019
    detail.hit.zdb_id: 7233-3
    detail.hit.zdb_id: 2006858-X
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  • 3
    Online Resource
    Online Resource
    First M87 Event Horizon Telescope Results. II. Array and Instrumentation
    American Astronomical Society ; 2019
    In:  The Astrophysical Journal Letters Vol. 875, No. 1 ( 2019-04-10), p. L2-
    Details
    In: The Astrophysical Journal Letters, American Astronomical Society, Vol. 875, No. 1 ( 2019-04-10), p. L2-
    Abstract: The Event Horizon Telescope (EHT) is a very long baseline interferometry (VLBI) array that comprises millimeter- and submillimeter-wavelength telescopes separated by distances comparable to the diameter of the Earth. At a nominal operating wavelength of ∼1.3 mm, EHT angular resolution ( λ / D ) is ∼25 μ as, which is sufficient to resolve nearby supermassive black hole candidates on spatial and temporal scales that correspond to their event horizons. With this capability, the EHT scientific goals are to probe general relativistic effects in the strong-field regime and to study accretion and relativistic jet formation near the black hole boundary. In this Letter we describe the system design of the EHT, detail the technology and instrumentation that enable observations, and provide measures of its performance. Meeting the EHT science objectives has required several key developments that have facilitated the robust extension of the VLBI technique to EHT observing wavelengths and the production of instrumentation that can be deployed on a heterogeneous array of existing telescopes and facilities. To meet sensitivity requirements, high-bandwidth digital systems were developed that process data at rates of 64 gigabit s −1 , exceeding those of currently operating cm-wavelength VLBI arrays by more than an order of magnitude. Associated improvements include the development of phasing systems at array facilities, new receiver installation at several sites, and the deployment of hydrogen maser frequency standards to ensure coherent data capture across the array. These efforts led to the coordination and execution of the first Global EHT observations in 2017 April, and to event-horizon-scale imaging of the supermassive black hole candidate in M87.
    Type of Medium: Online Resource
    ISSN: 2041-8205 , 2041-8213
    URL: Article
    DOI: 10.3847/2041-8213/ab0c96
    Language: Unknown
    Publisher: American Astronomical Society
    Publication Date: 2019
    detail.hit.zdb_id: 7233-3
    detail.hit.zdb_id: 2006858-X
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  • 4
    Online Resource
    Online Resource
    A Search for Pulsars around Sgr A* in the First Event Horizon Telescope Data Set
    American Astronomical Society ; 2023
    In:  The Astrophysical Journal Vol. 959, No. 1 ( 2023-12-01), p. 14-
    Details
    In: The Astrophysical Journal, American Astronomical Society, Vol. 959, No. 1 ( 2023-12-01), p. 14-
    Abstract: In 2017 the Event Horizon Telescope (EHT) observed the supermassive black hole at the center of the Milky Way, Sagittarius A* (Sgr A*), at a frequency of 228.1 GHz ( λ = 1.3 mm). The fundamental physics tests that even a single pulsar orbiting Sgr A* would enable motivate searching for pulsars in EHT data sets. The high observing frequency means that pulsars—which typically exhibit steep emission spectra—are expected to be very faint. However, it also negates pulse scattering, an effect that could hinder pulsar detections in the Galactic center. Additionally, magnetars or a secondary inverse Compton emission could be stronger at millimeter wavelengths than at lower frequencies. We present a search for pulsars close to Sgr A* using the data from the three most sensitive stations in the EHT 2017 campaign: the Atacama Large Millimeter/submillimeter Array, the Large Millimeter Telescope, and the IRAM 30 m Telescope. We apply three detection methods based on Fourier-domain analysis, the fast folding algorithm, and single-pulse searches targeting both pulsars and burst-like transient emission. We use the simultaneity of the observations to confirm potential candidates. No new pulsars or significant bursts were found. Being the first pulsar search ever carried out at such high radio frequencies, we detail our analysis methods and give a detailed estimation of the sensitivity of the search. We conclude that the EHT 2017 observations are only sensitive to a small fraction (≲2.2%) of the pulsars that may exist close to Sgr A*, motivating further searches for fainter pulsars in the region.
    Type of Medium: Online Resource
    ISSN: 0004-637X , 1538-4357
    URL: Article
    DOI: 10.3847/1538-4357/acf4f2
    RVK:
    UA 1000
    Language: Unknown
    Publisher: American Astronomical Society
    Publication Date: 2023
    detail.hit.zdb_id: 2960-9
    detail.hit.zdb_id: 1473835-1
    SSG: 16,12
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  • 5
    Online Resource
    Online Resource
    Experimental Demonstration of Microwave Two-Dimensional Airy Beam Generation Based on Single-Layer Metasurface
    Institute of Electrical and Electronics Engineers (IEEE) ; 2020
    In:  IEEE Transactions on Antennas and Propagation Vol. 68, No. 11 ( 2020-11), p. 7507-7516
    Details
    In: IEEE Transactions on Antennas and Propagation, Institute of Electrical and Electronics Engineers (IEEE), Vol. 68, No. 11 ( 2020-11), p. 7507-7516
    Type of Medium: Online Resource
    ISSN: 0018-926X , 1558-2221
    URL: Journal
    URL: Article
    DOI: 10.1109/TAP.8
    DOI: 10.1109/TAP.2020.2996826
    Language: Unknown
    Publisher: Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2020
    detail.hit.zdb_id: 218496-5
    detail.hit.zdb_id: 2027421-X
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  • 6
    Online Resource
    Online Resource
    Broadband Multi-wavelength Properties of M87 during the 2017 Event Horizon Telescope Campaign
    American Astronomical Society ; 2021
    In:  The Astrophysical Journal Letters Vol. 911, No. 1 ( 2021-04-01), p. L11-
    Details
    In: The Astrophysical Journal Letters, American Astronomical Society, Vol. 911, No. 1 ( 2021-04-01), p. L11-
    Abstract: In 2017, the Event Horizon Telescope (EHT) Collaboration succeeded in capturing the first direct image of the center of the M87 galaxy. The asymmetric ring morphology and size are consistent with theoretical expectations for a weakly accreting supermassive black hole of mass ∼6.5 × 10 9 M ⊙ . The EHTC also partnered with several international facilities in space and on the ground, to arrange an extensive, quasi-simultaneous multi-wavelength campaign. This Letter presents the results and analysis of this campaign, as well as the multi-wavelength data as a legacy data repository. We captured M87 in a historically low state, and the core flux dominates over HST-1 at high energies, making it possible to combine core flux constraints with the more spatially precise very long baseline interferometry data. We present the most complete simultaneous multi-wavelength spectrum of the active nucleus to date, and discuss the complexity and caveats of combining data from different spatial scales into one broadband spectrum. We apply two heuristic, isotropic leptonic single-zone models to provide insight into the basic source properties, but conclude that a structured jet is necessary to explain M87’s spectrum. We can exclude that the simultaneous γ -ray emission is produced via inverse Compton emission in the same region producing the EHT mm-band emission, and further conclude that the γ -rays can only be produced in the inner jets (inward of HST-1) if there are strongly particle-dominated regions. Direct synchrotron emission from accelerated protons and secondaries cannot yet be excluded.
    Type of Medium: Online Resource
    ISSN: 2041-8205 , 2041-8213
    URL: Article
    DOI: 10.3847/2041-8213/abef71
    Language: Unknown
    Publisher: American Astronomical Society
    Publication Date: 2021
    detail.hit.zdb_id: 7233-3
    detail.hit.zdb_id: 2006858-X
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  • 7
    Online Resource
    Online Resource
    Polarimetric Geometric Modeling for mm-VLBI Observations of Black Holes
    American Astronomical Society ; 2023
    In:  The Astrophysical Journal Letters Vol. 957, No. 2 ( 2023-11-01), p. L21-
    Details
    In: The Astrophysical Journal Letters, American Astronomical Society, Vol. 957, No. 2 ( 2023-11-01), p. L21-
    Abstract: The Event Horizon Telescope (EHT) is a millimeter very long baseline interferometry (VLBI) array that has imaged the apparent shadows of the supermassive black holes M87* and Sagittarius A*. Polarimetric data from these observations contain a wealth of information on the black hole and accretion flow properties. In this work, we develop polarimetric geometric modeling methods for mm-VLBI data, focusing on approaches that fit data products with differing degrees of invariance to broad classes of calibration errors. We establish a fitting procedure using a polarimetric “m-ring” model to approximate the image structure near a black hole. By fitting this model to synthetic EHT data from general relativistic magnetohydrodynamic models, we show that the linear and circular polarization structure can be successfully approximated with relatively few model parameters. We then fit this model to EHT observations of M87* taken in 2017. In total intensity and linear polarization, the m-ring fits are consistent with previous results from imaging methods. In circular polarization, the m-ring fits indicate the presence of event-horizon-scale circular polarization structure, with a persistent dipolar asymmetry and orientation across several days. The same structure was recovered independently of observing band, used data products, and model assumptions. Despite this broad agreement, imaging methods do not produce similarly consistent results. Our circular polarization results, which imposed additional assumptions on the source structure, should thus be interpreted with some caution. Polarimetric geometric modeling provides a useful and powerful method to constrain the properties of horizon-scale polarized emission, particularly for sparse arrays like the EHT.
    Type of Medium: Online Resource
    ISSN: 2041-8205 , 2041-8213
    URL: Article
    DOI: 10.3847/2041-8213/acff6f
    Language: Unknown
    Publisher: American Astronomical Society
    Publication Date: 2023
    detail.hit.zdb_id: 7233-3
    detail.hit.zdb_id: 2006858-X
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  • 8
    Online Resource
    Online Resource
    Fluorescence quenching determination of tetracyclines based on the synergistic oxidation effect between Fe 3 O 4 nanoparticles and tetracyclines
    IOP Publishing ; 2023
    In:  Methods and Applications in Fluorescence Vol. 11, No. 3 ( 2023-07-01), p. 035001-
    Details
    In: Methods and Applications in Fluorescence, IOP Publishing, Vol. 11, No. 3 ( 2023-07-01), p. 035001-
    Abstract: In recent years, tetracyclines (TCs) is a hot research topic. Herein, we report an interesting discovery using the complexation of oxytetracycline and metal ions. In this study, according to the properties of Fe 3 O 4 nanoparticles (Fe 3 O 4 NPs) as a nanoenzyme, it can be used to catalyze the oxidation of KI by H 2 O 2 to produce I 3 − , while at the same time I 3 − binds to rhodamine 6G (Rh6G) to form a conjoined particle (Rh6G ∼ I 3 ) n , leading to a decrease in the fluorescence intensity of Rh6G. However, in the presence of TCs, Fe 3 O 4 NPs have a synergistic effect with TCs, leading to enhanced catalytic activity, as well as better selectivity compared to the activity of other reducing enzymes. Consequently,the fluorescent signal based on a resonance scattering effect between Rh6G and I 3 − is dependent on the concentration of TCs, thus achieving highly facile and robust detection of TCs. The limits of detection (LOD) of the method were 20 nM, 10 nM and 40 nM for oxytetracycline(OTC), tetracycline(TC) and chlortetracycline(CTC), respectively. Most importantly, the method can be successfully applied to the detection of TCs in milk, eggs, and honey. The recoveries of spiked samples ranged from 83.11 to 118.95%. Thus, a stable, hands-on strategy for the detection of TCs is proposed, which has potential applications in the field of food safety and environmental protection.
    Type of Medium: Online Resource
    ISSN: 2050-6120
    URL: Article
    DOI: 10.1088/2050-6120/acca61
    Language: Unknown
    Publisher: IOP Publishing
    Publication Date: 2023
    detail.hit.zdb_id: 2700785-6
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  • 9
    Online Resource
    Online Resource
    Data_Sheet_1.PDF
    Frontiers Media SA ; 2022
    In:  Frontiers in Aging Neuroscience Vol. 14 ( 2022-5-23)
    Details
    In: Frontiers in Aging Neuroscience, Frontiers Media SA, Vol. 14 ( 2022-5-23)
    Abstract: Eosinophils contribute to antibacterial defense by releasing mitochondrial DNA, which are decreased in patients with acute ischemic stroke (AIS). However, the impact of eosinophils on stroke-associated pneumonia (SAP) among patients with AIS remains unclear. Moreover, whether SAP is in the path of the association between eosinophils and clinical outcomes also remains unclear. We aimed to assess the relationships between eosinophils, SAP, and clinical outcome after mechanical thrombectomy in patients with AIS. Methods A total of 328 consecutive patients with AIS who underwent mechanical thrombectomy between May 2017 and March 2021 were analyzed. Their baseline data and peripheral eosinophil counts were recorded on admission. Regression analysis was used to assess the effect of eosinophils on SAP, and its effect on poor outcome is defined as a modified Rankin Scale score of 3–6 at month 3 after admission. Mediation analysis was utilized to assess the proportion of the total effect of SAP on the association between eosinophils and poor outcomes. Results Multivariate analysis revealed that eosinophils was independently associated with SAP after adjusting for potential confounders (odds ratio, 0.00; 95% CI, 0.00–0.38; P = 0.0267), which are consistent with the result of eosinophils (dichotomous) as a categorical variable (odds ratio, 0.54; 95% CI, 0.31–0.96; P = 0.0342). A non-linear relationship was detected between eosinophils and SAP, whose inflection point was 0.06. Subgroup analyses further confirmed these associations. Eosinophils were also associated with poor outcomes (odds ratio, 0.00; 95% CI, 0.00–0.14; P = 0.0124). Additionally, mediation analysis found that SAP partially mediated the negative relationship between eosinophils and poor outcome (indirect effect = −0.169; 95% CI:−0.339 –−0.040, P & lt; 0.001). Conclusion Our findings suggested that a lower eosinophil level was associated with higher SAP and poorer outcome, and SAP might play an important effect in the association between eosinophils and poor outcomes.
    Type of Medium: Online Resource
    ISSN: 1663-4365
    URL: Article
    URL: Article
    DOI: 10.3389/fnagi.2022.830858
    DOI: 10.3389/fnagi.2022.830858.s001
    Language: Unknown
    Publisher: Frontiers Media SA
    Publication Date: 2022
    detail.hit.zdb_id: 2558898-9
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  • 10
    Online Resource
    Online Resource
    A 16-Gb, 18-Gb/s/pin GDDR6 DRAM With Per-Bit Trainable Single-Ended DFE and PLL-Less Clocking
    Institute of Electrical and Electronics Engineers (IEEE) ; 2019
    In:  IEEE Journal of Solid-State Circuits Vol. 54, No. 1 ( 2019-1), p. 197-209
    Details
    In: IEEE Journal of Solid-State Circuits, Institute of Electrical and Electronics Engineers (IEEE), Vol. 54, No. 1 ( 2019-1), p. 197-209
    Type of Medium: Online Resource
    ISSN: 0018-9200 , 1558-173X
    URL: Article
    DOI: 10.1109/JSSC.2018.2883395
    Language: Unknown
    Publisher: Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2019
    detail.hit.zdb_id: 240580-5
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