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- Algaba Brazalez, Astrid, 1983, et al.
(author)
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Improved Microstrip Filters Using PMC Packaging by Lid of Nails
- 2012
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In: IEEE Transactions on Components, Packaging and Manufacturing Technology. - 2156-3985 .- 2156-3950. ; 2:7, s. 1075-1084
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Journal article (peer-reviewed)abstract
- This paper shows that microstrip filters perform like textbook examples when packaged with perfect magnetic conductor (PMC). A PMC is made as a pin surface or lid of nails, and this is used to package a microstrip parallel coupled line bandpass filter. Our measurements confirm that parallel plate, cavity modes, and radiation are suppressed. This paper also includes a study of the reasons for a frequency shift between the ideal PMC packaged case and the realized case.
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| 4. |
- Akiyama, Kazunori, et al.
(author)
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First Sagittarius A* Event Horizon Telescope Results. II. EHT and Multiwavelength Observations, Data Processing, and Calibration
- 2022
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In: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8213 .- 2041-8205. ; 930:2
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Journal article (peer-reviewed)abstract
- We present Event Horizon Telescope (EHT) 1.3 mm measurements of the radio source located at the position of the supermassive black hole Sagittarius A* (Sgr A*), collected during the 2017 April 5-11 campaign. The observations were carried out with eight facilities at six locations across the globe. Novel calibration methods are employed to account for Sgr A*'s flux variability. The majority of the 1.3 mm emission arises from horizon scales, where intrinsic structural source variability is detected on timescales of minutes to hours. The effects of interstellar scattering on the image and its variability are found to be subdominant to intrinsic source structure. The calibrated visibility amplitudes, particularly the locations of the visibility minima, are broadly consistent with a blurred ring with a diameter of similar to 50 mu as, as determined in later works in this series. Contemporaneous multiwavelength monitoring of Sgr A* was performed at 22, 43, and 86 GHz and at near-infrared and X-ray wavelengths. Several X-ray flares from Sgr A* are detected by Chandra, one at low significance jointly with Swift on 2017 April 7 and the other at higher significance jointly with NuSTAR on 2017 April 11. The brighter April 11 flare is not observed simultaneously by the EHT but is followed by a significant increase in millimeter flux variability immediately after the X-ray outburst, indicating a likely connection in the emission physics near the event horizon. We compare Sgr A*'s broadband flux during the EHT campaign to its historical spectral energy distribution and find that both the quiescent emission and flare emission are consistent with its long-term behavior.
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| 5. |
- Akiyama, Kazunori, et al.
(author)
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First Sagittarius A* Event Horizon Telescope Results. III. Imaging of the Galactic Center Supermassive Black Hole
- 2022
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In: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8213 .- 2041-8205. ; 930:2
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Journal article (peer-reviewed)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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| 6. |
- Georgi, Richard, 1987
(author)
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Peace that antagonizes: Reading Colombia's peace process as hegemonic crisis
- 2023
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In: Security Dialogue. - : SAGE Publications. - 0967-0106 .- 1460-3640. ; 54:2, s. 173-191
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Journal article (peer-reviewed)abstract
- This article explores how disruptive political conflicts evolve in peace processes by studying Colombian human rights defenders' discourses about the peace process with the FARC-EP. While post-conflict scholarship has predominantly discussed violence and societal frictions as caused by legacies of war or flawed peace governance, I focus on the confrontations over political imaginaries that are endemic to peace processes. Through the lens of post-foundational discourse theory, I read the peace process as hegemonic crisis. This allows me to unpack the entanglement of political change and conflict, to which my discussions with human rights defenders allude: On the one hand, the peace agreement opened a political moment, in which it seemed possible to leave behind the hitherto hegemonic imaginary of the conflict as terrorism that had protracted the 'state of war'; the advocacy for peace with social justice, on the other hand, it restaged historical confrontations with elites of the political right as antagonistic conflict over the meaning of peace. My analysis not only challenges the paradigm of war-to-peace transition, but also defines discursive conditions under which disruptive conflicts turn a peace process into an enduring interregnum, where the dawn of the post-conflict epoch is perpetually deferred and activist lives are threatened.
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- Janson, Tore, 1936-
(author)
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Vocative and the grammar of calls
- 2013
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In: Vocative!. - Berlin : Mouton de Gruyter. - 9783110303896 ; , s. 219-234
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Book chapter (peer-reviewed)abstract
- Vocative forms appear in calls, which constitute a type of utterances; other types are statements, questions, and commands. Grammatical descriptions usually focus on sentences, the grammatical form of statements. This paper presents a sketch of the grammar of calls. The basic form of a call is a noun phrase denoting a person. Calls may include special marking to show the utterance type. There may be markers outside the noun phrase (utterance marking) or marking within the noun phrase (noun phrase marking). Some languages have one of the types and some have both. The types typically do not interfere but occur independently of each other. Utterance marking consists of special intonation or of an optional vocalic particle. Noun phrase marking may consist of suppletion, contraction or apocope of the noun, or of addition of an affix. The noun then has a special vocative form. In languages with obligatory case marking, noun marking of calls and marking of case may interfere in complex ways.
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