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Träfflista för sökning "WFRF:(Oh S. H.) ;hsvcat:2"

Sökning: WFRF:(Oh S. H.) > Teknik

  • Resultat 1-7 av 7
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1.
  • Georgiev, Boris, et al. (författare)
  • A Universal Power-law Prescription for Variability from Synthetic Images of Black Hole Accretion Flows
  • 2022
  • Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8213 .- 2041-8205. ; 930:2
  • Tidskriftsartikel (refereegranskat)abstract
    • We present a framework for characterizing the spatiotemporal power spectrum of the variability expected from the horizon-scale emission structure around supermassive black holes, and we apply this framework to a library of general relativistic magnetohydrodynamic (GRMHD) simulations and associated general relativistic ray-traced images relevant for Event Horizon Telescope (EHT) observations of Sgr A*. We find that the variability power spectrum is generically a red-noise process in both the temporal and spatial dimensions, with the peak in power occurring on the longest timescales and largest spatial scales. When both the time-averaged source structure and the spatially integrated light-curve variability are removed, the residual power spectrum exhibits a universal broken power-law behavior. On small spatial frequencies, the residual power spectrum rises as the square of the spatial frequency and is proportional to the variance in the centroid of emission. Beyond some peak in variability power, the residual power spectrum falls as that of the time-averaged source structure, which is similar across simulations; this behavior can be naturally explained if the variability arises from a multiplicative random field that has a steeper high-frequency power-law index than that of the time-averaged source structure. We briefly explore the ability of power spectral variability studies to constrain physical parameters relevant for the GRMHD simulations, which can be scaled to provide predictions for black holes in a range of systems in the optically thin regime. We present specific expectations for the behavior of the M87* and Sgr A* accretion flows as observed by the EHT.
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2.
  • Akiyama, Kazunori, et al. (författare)
  • First Sagittarius A* Event Horizon Telescope Results. III. Imaging of the Galactic Center Supermassive Black Hole
  • 2022
  • Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8213 .- 2041-8205. ; 930:2
  • Tidskriftsartikel (refereegranskat)abstract
    • We present the first event-horizon-scale images and spatiotemporal analysis of Sgr A* taken with the Event Horizon Telescope in 2017 April at a wavelength of 1.3 mm. Imaging of Sgr A* has been conducted through surveys over a wide range of imaging assumptions using the classical CLEAN algorithm, regularized maximum likelihood methods, and a Bayesian posterior sampling method. Different prescriptions have been used to account for scattering effects by the interstellar medium toward the Galactic center. Mitigation of the rapid intraday variability that characterizes Sgr A* has been carried out through the addition of a "variability noise budget" in the observed visibilities, facilitating the reconstruction of static full-track images. Our static reconstructions of Sgr A* can be clustered into four representative morphologies that correspond to ring images with three different azimuthal brightness distributions and a small cluster that contains diverse nonring morphologies. Based on our extensive analysis of the effects of sparse (u, v)-coverage, source variability, and interstellar scattering, as well as studies of simulated visibility data, we conclude that the Event Horizon Telescope Sgr A* data show compelling evidence for an image that is dominated by a bright ring of emission with a ring diameter of similar to 50 mu as, consistent with the expected "shadow" of a 4 x 10(6) M (circle dot) black hole in the Galactic center located at a distance of 8 kpc.
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3.
  • Broderick, Avery E., et al. (författare)
  • Characterizing and Mitigating Intraday Variability: Reconstructing Source Structure in Accreting Black Holes with mm-VLBI
  • 2022
  • Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8213 .- 2041-8205. ; 930:2
  • Tidskriftsartikel (refereegranskat)abstract
    • The extraordinary physical resolution afforded by the Event Horizon Telescope has opened a window onto the astrophysical phenomena unfolding on horizon scales in two known black holes, M87* and Sgr A*. However, with this leap in resolution has come a new set of practical complications. Sgr A* exhibits intraday variability that violates the assumptions underlying Earth aperture synthesis, limiting traditional image reconstruction methods to short timescales and data sets with very sparse (u, v) coverage. We present a new set of tools to detect and mitigate this variability. We develop a data-driven, model-agnostic procedure to detect and characterize the spatial structure of intraday variability. This method is calibrated against a large set of mock data sets, producing an empirical estimator of the spatial power spectrum of the brightness fluctuations. We present a novel Bayesian noise modeling algorithm that simultaneously reconstructs an average image and statistical measure of the fluctuations about it using a parameterized form for the excess variance in the complex visibilities not otherwise explained by the statistical errors. These methods are validated using a variety of simulated data, including general relativistic magnetohydrodynamic simulations appropriate for Sgr A* and M87*. We find that the reconstructed source structure and variability are robust to changes in the underlying image model. We apply these methods to the 2017 EHT observations of M87*, finding evidence for variability across the EHT observing campaign. The variability mitigation strategies presented are widely applicable to very long baseline interferometry observations of variable sources generally, for which they provide a data-informed averaging procedure and natural characterization of inter-epoch image consistency.
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4.
  • Junesch, Juliane, 1987, et al. (författare)
  • Location-specific nanoplasmonic sensing of biomolecular binding to lipid membranes with negative curvature
  • 2015
  • Ingår i: Nanoscale. - : Royal Society of Chemistry (RSC). - 2040-3372 .- 2040-3364. ; 7:37, s. 15080-15085
  • Tidskriftsartikel (refereegranskat)abstract
    • The biochemical processes of cell membranes are sensitive to the geometry of the lipid bilayer. We show how plasmonic "nanowells" provide label-free real-time analysis of molecules on membranes with detection of preferential binding at negative curvature. It is demonstrated that norovirus accumulate in invaginations due to multivalent interactions with glycosphingolipids.
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5.
  • Dahlin, Andreas, 1980, et al. (författare)
  • Promises and challenges of nanoplasmonic devices for refractometric biosensing
  • 2013
  • Ingår i: Nanophotonics. - : Walter de Gruyter GmbH. - 2192-8614 .- 2192-8606. ; 2:2, s. 83-101
  • Tidskriftsartikel (refereegranskat)abstract
    • Optical biosensors based on surface plasmon resonance (SPR) in metallic thin films are currently standard tools for measuring molecular binding kinetics and affinities - an important task for biophysical studies and pharmaceutical development. Motivated by recent progress in the design and fabrication of metallic nanostructures, such as nanoparticles or nanoholes of various shapes, researchers have been pursuing a new generation of biosensors harnessing tailored plasmonic effects in these engineered nanostructures. Nanoplasmonic devices, while demanding nanofabrication, offer tunability with respect to sensor dimension and physical properties, thereby enabling novel biological interfacing opportunities and extreme miniaturization. Here we provide an integrated overview of refractometric biosensing with nanoplasmonic devices and highlight some recent examples of nanoplasmonic sensors capable of unique functions that are difficult to accomplish with conventional SPR. For example, since the local field strength and spatial distribution can be readily tuned by varying the shape and arrangement of nanostructures, biomolecular interactions can be controlled to occur in regions of high field strength. This may improve signal-to-noise and also enable sensing a small number of molecules. Furthermore, the nanoscale plasmonic sensor elements may, in combination with nanofabrication and materials-selective surface-modifications, make it possible to merge affinity biosensing with nanofluidic liquid handling.
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6.
  • Hsu, L. H., et al. (författare)
  • Design, Fabrication, and Reliability of Low-Cost Flip-Chip-On-Board Package for Commercial Applications up to 50 GHz
  • 2012
  • Ingår i: IEEE Transactions on Components, Packaging and Manufacturing Technology. - 2156-3985 .- 2156-3950. ; 2:3, s. 402-409
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper presents a flip-chip-on-board (FCOB) packaging technology using a Rogers RO3210 laminate for microwave applications. Compared to the conventional microwave packaging architecture, the proposed FCOB technology skips one level of the ceramic package and thus results in lower reflections and manufacturing costs. To fulfill the small dimension requirement on printed circuit boards, the coplanar waveguide (CPW) transmission line and flip-chip bump were fabricated on a high-k RO3210 board (epsilon(r) = 10.2) with photolithography and electroplating. The GaAs chip patterned with the CPW line was then flip-chip-mounted onto the RO3210 laminate board. This structure displayed excellent performance from dc to 50 GHz with a return loss S-11 greater than 18 dB and insertion loss S-21 less than 0.5 dB. Meanwhile, the flip-chip bonding of the in-house-fabricated In0.52Al0.As-48/In0.6Ga0.4As metamorphic high-electron-mobility transistor devices on RO3210 also displayed excellent gain performance with a small degradation of 1 dB from dc to 40 GHz, showing the potential of implementing microwave integrated circuits on RO3210. To enhance the mechanical reliability, an epoxy-based underfill was injected into the flip-chip assemblies. Thermal cycling tests were performed to test the interconnect reliability, and the results indicated that the samples passed the thermal cycling test at least up to 600 cycles, showing excellent reliability for commercial applications. To the best of the authors' knowledge, this is the first study that evaluates the use of the RO3210 laminate for microwave flip-chip in open literature.
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7.
  • Mazzotta, Francesco, 1985, et al. (författare)
  • Influence of the Evanescent Field Decay Length on the Sensitivity of Plasmonic Nanodisks and Nanoholes
  • 2015
  • Ingår i: ACS Photonics. - : American Chemical Society (ACS). - 2330-4022. ; 2:2, s. 256-262
  • Tidskriftsartikel (refereegranskat)abstract
    • We evaluate and compare the sensitivity of gold nanodisks on silica substrates and nanoholes made in silica-supported gold films, two of the most common sensor structures used in plasmonic biosensing. An alumina overcoat was applied by atomic layer deposition (ALD) to precisely control the interfacial refractive index and determine the evanescent plasmonic field decay length. The results are in good agreement with analytical models and biomolecular binding experiments for the two substrates. We found that nanodisks outperform nanoholes for thin dielectric coatings (similar to 20 nm). The optimum nanoplasmonic transducer element for a given biorecognition reaction can be chosen based on experimentally determined bulk sensitivities/noise levels and theoretically estimated evanescent field decay lengths.
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  • Resultat 1-7 av 7

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