| 1. |
- Akiyama, Kazunori, et al.
(författare)
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First M87 Event Horizon Telescope Results. I. the Shadow of the Supermassive Black Hole
- 2019
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Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8213 .- 2041-8205. ; 875:1
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Tidskriftsartikel (refereegranskat)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 μas, 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 o . 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.
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| 2. |
- Akiyama, Kazunori, et al.
(författare)
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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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Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8213 .- 2041-8205. ; 930:2
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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. |
- Akiyama, Kazunori, et al.
(författare)
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First Sagittarius A* Event Horizon Telescope Results. IV. Variability, Morphology, and Black Hole Mass
- 2022
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Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8213 .- 2041-8205. ; 930:2
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we quantify the temporal variability and image morphology of the horizon-scale emission from Sgr A*, as observed by the EHT in 2017 April at a wavelength of 1.3 mm. We find that the Sgr A* data exhibit variability that exceeds what can be explained by the uncertainties in the data or by the effects of interstellar scattering. The magnitude of this variability can be a substantial fraction of the correlated flux density, reaching similar to 100% on some baselines. Through an exploration of simple geometric source models, we demonstrate that ring-like morphologies provide better fits to the Sgr A* data than do other morphologies with comparable complexity. We develop two strategies for fitting static geometric ring models to the time-variable Sgr A* data; one strategy fits models to short segments of data over which the source is static and averages these independent fits, while the other fits models to the full data set using a parametric model for the structural variability power spectrum around the average source structure. Both geometric modeling and image-domain feature extraction techniques determine the ring diameter to be 51.8 +/- 2.3 mu as (68% credible intervals), with the ring thickness constrained to have an FWHM between similar to 30% and 50% of the ring diameter. To bring the diameter measurements to a common physical scale, we calibrate them using synthetic data generated from GRMHD simulations. This calibration constrains the angular size of the gravitational radius to be 4.8(-0.7)(+1.4) mu as, which we combine with an independent distance measurement from maser parallaxes to determine the mass of Sgr A* to be 4.0(-0.6)(+1.1) x 10(6) M-circle dot.
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| 4. |
- Akiyama, Kazunori, et al.
(författare)
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First Sagittarius A* Event Horizon Telescope Results. V. Testing Astrophysical Models of the Galactic Center Black Hole
- 2022
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Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8213 .- 2041-8205. ; 930:2
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we provide a first physical interpretation for the Event Horizon Telescope's (EHT) 2017 observations of Sgr A*. Our main approach is to compare resolved EHT data at 230 GHz and unresolved non-EHT observations from radio to X-ray wavelengths to predictions from a library of models based on time-dependent general relativistic magnetohydrodynamics simulations, including aligned, tilted, and stellar-wind-fed simulations; radiative transfer is performed assuming both thermal and nonthermal electron distribution functions. We test the models against 11 constraints drawn from EHT 230 GHz data and observations at 86 GHz, 2.2 mu m, and in the X-ray. All models fail at least one constraint. Light-curve variability provides a particularly severe constraint, failing nearly all strongly magnetized (magnetically arrested disk (MAD)) models and a large fraction of weakly magnetized models. A number of models fail only the variability constraints. We identify a promising cluster of these models, which are MAD and have inclination i <= 30 degrees. They have accretion rate (5.2-9.5) x 10(-9) M (circle dot) yr(-1), bolometric luminosity (6.8-9.2) x 10(35) erg s(-1), and outflow power (1.3-4.8) x 10(38) erg s(-1). We also find that all models with i >= 70 degrees fail at least two constraints, as do all models with equal ion and electron temperature; exploratory, nonthermal model sets tend to have higher 2.2 mu m flux density; and the population of cold electrons is limited by X-ray constraints due to the risk of bremsstrahlung overproduction. Finally, we discuss physical and numerical limitations of the models, highlighting the possible importance of kinetic effects and duration of the simulations.
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| 5. |
- Algaba Brazalez, Astrid, 1983, et al.
(författare)
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Improving microstrip filters with gap waveguide packaging
- 2011
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Ingår i: Proceedings of the 5th European Conference on Antennas and Propagation, EUCAP 2011. Rome, 11-15 April 2011. - 9781457702501 ; , s. 1080-1084
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Konferensbidrag (refereegranskat)abstract
- A study is presented of the performance of microstrip filters packaged with Perfect Magnetic Conductor (PMC) and realization of the PMC using a lid of nails. A 3rd order parallel coupled-line bandpass filter is designed and packaged with a lid of nails at the Ku-band. The study shows the PMC packaging technique is very efficient in improving the filter characteristics including the insertion loss in the bandpass region.
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| 6. |
- Chamzas, Constantinos, et al.
(författare)
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Comparing Reconstruction- and Contrastive-based Models for Visual Task Planning
- 2022
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Ingår i: 2022 IEEE/RSJ INTERNATIONAL CONFERENCE ON INTELLIGENT ROBOTS AND SYSTEMS (IROS). - : Institute of Electrical and Electronics Engineers (IEEE). ; , s. 12550-12557
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Konferensbidrag (refereegranskat)abstract
- Learning state representations enables robotic planning directly from raw observations such as images. Several methods learn state representations by utilizing losses based on the reconstruction of the raw observations from a lower-dimensional latent space. The similarity between observations in the space of images is often assumed and used as a proxy for estimating similarity between the underlying states of the system. However, observations commonly contain task-irrelevant factors of variation which are nonetheless important for reconstruction, such as varying lighting and different camera viewpoints. In this work, we define relevant evaluation metrics and perform a thorough study of different loss functions for state representation learning. We show that models exploiting task priors, such as Siamese networks with a simple contrastive loss, outperform reconstruction-based representations in visual task planning in case of task-irrelevant factors of variations.
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| 7. |
- Janson, Ulla, et al.
(författare)
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Riva, cirkulera, bygga nytt eller renovera? Energianvändning i hela livscykeln.
- 2022
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Bostads- och servicesektorn i Sverige står idag för ungefär 40% av Sveriges totalaårliga energibehov (Energimyndigheten, 2021). Förutom detta används en stormängd energi för nyproduktion, underhåll och rivning av byggnader. Att minskaenergianvändningen i byggsektorns hela livscykel är en nyckel för att nå uppsattaenergi- och klimatmål. I detta projekt analyseras vad som är bäst ur ettenergiperspektiv, men även avseende global uppvärmningspotential, om enbefintlig byggnad antingen ska rivas och ersättas med en ny energieffektiv ellerom den ska renoveras och isåfall hur.Ett faktiskt projekt i centrala Lund ligger till grund för analysen. Fem huskropparpå fastigheten Sjuksystern 2, en del av sjukhusområdet, behöver rivas för att geplats för sjukhusets vidare expansion. En analys har utförts avseende energibehovför uppvärmning vid olika renoveringsåtgärder, möjlighet till återbruk av materialoch nyproduktion av byggnad med samma utformning som den befintliga.Analysen utgår från de kulturvärden som finns i byggnaderna och platsen.Eventuella renoveringsåtgärder och gestaltningen av den nya byggnaden somanalyseras är alla utförda för att bibehålla de kulturvärden som framkommit vidintervjuer av tidigare brukare och arbetare på platsen, besiktning av byggnaderoch inventering av platsen.Både mjuka och hårda kulturvärden lyftes fram, där några av de mjuka värdenaöversattes till hårda värden, för att kunna inkludera i de framtida byggnaderna.3 (52)Energibehov för uppvärmning beräknades för den befintliga byggnaden, vid valdaenergieffektiviserande åtgärder och för en nyproducerad, mycket energieffektivbyggnad. Global uppvärmningspotential beräknades även för de olikaalternativen.Resultatet visar att det går att minska energibehovet vid renovering med upp tillhälften av det ursprungliga behovet med åtgärder som bibehåller kulturvärden;vindsisolering, invändig ytterväggsisolering, installation av FTX och byte avfönster. Ett alternativ till fönsterbyte är att byta den inre glasrutan mot englaskassett. Energibehovet för uppvärmning minskar betydande även för dettaalternativ, samtidigt som kulturvärden i befintliga fönster kan behållas.Vid beräkning av global uppvärmningspotential (GWP) för de olikaenergieffektiviserande åtgärderna har val av energimix för uppvärmningavgörande betydelse. GWP från valda material är också avgörande för resultatet.För att de åtgärder som minskar energibehovet för uppvärmning mest ska minskatotal GWP behöver åtgärderna för ett energiscenario med låg GWP vara utfördamed material med låg GWP. För alla andra energiscenarion minskar GWP ävenför åtgärder utförda med material med högt GWP.Vid behov av åtgärd på fönster testades alternativen att behålla, byta innerglas tillLE-ruta, byta innerglas till glaskassett eller att byta fönstret. Att sätta in englaskassett beräknas till att minska energibehovet med 8%, jämfört med 13% förett nytt fönster. Beroende på val av energimix ger de olika åtgärderna olikaresultat för GWP. Värt att notera är att installation av ett nytt fönster kan innebäraen högre total GWP trots avsevärd energieffektivisering medan en glaskassettalltid ger en lägre GWP oavsett val av energiscenario.Beroende på val av energiscenario kan GWP från en nyproducerad mycketenergieffektiv byggnad vara högre än vid renovering av en befintlig. Även om ennybyggnad har en lägre energianvändning än den befintliga byggnaden såresulterar en nybyggnad i högre GWP, vid energiscenario I-III som används idenna studie. Återbruk av tegel ger en något lägre GWP vid nyproduktion avbyggnad. Det möjliggör dessutom bevarande av kulturvärden vid en eventuellrivning av befintlig byggnad.
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| 8. |
- Kim, Jae-Kwang, 1978, et al.
(författare)
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An Imidazolium based ionic liquid electrolyte for lithium batteries
- 2010
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Ingår i: Journal of Power Sources. - : Elsevier BV. - 0378-7753. ; 195:22, s. 7639-7643
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Tidskriftsartikel (refereegranskat)abstract
- An electrolyte for lithium batteries based on the ionic liquid 3-methy-1-propylimidazolium bis(trifluoromethysulfony)imide (PMIMTFSI) complexed with lithium bis(trifluoromethysulfony)imide (LiTFSI) at a molar ratio of 1:1 has been investigated. The electrolyte shows a high ionic conductivity (1.2 × 10−3 S cm−1) at room temperature. Over the whole investigated temperature range the ionic conductivity is more than one order of magnitude higher than for an analogue electrolyte based on N-butyl-N-methyl-pyrrolidinium bis(trifluoromethanesulfonyl)imide (Py14TFSI) complexed with LiTFSI and used here as a benchmark. Raman results indicate furthermore that the degree of lithium coordinated TFSI is slightly lower in the electrolyte based on PMIMTFSI and thus that the Li+ charge carriers should be higher than in electrolytes based on Py14TFSI. An ionic liquid gel electrolyte membrane was obtained by soaking a fibrous fully interconnected membrane, made of electrospun P(VdF-HFP), in the electrolyte. The gel electrolyte was cycled in Li/ionic liquid polymer electrolyte/Li cells over 15 days and in Li/LiFePO4 cells demonstrating good interfacial stability and highly stable discharge capacities with a retention of >96% after 50 cycles (146 mAh g−1).
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