| 1. |
- Wielgus, Maciek, et al.
(författare)
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Monitoring the Morphology of M87* in 2009-2017 with the Event Horizon Telescope
- 2020
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 1538-4357 .- 0004-637X. ; 901:1
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Tidskriftsartikel (refereegranskat)abstract
- The Event Horizon Telescope (EHT) has recently delivered the first resolved images of M87*, the supermassive black hole in the center of the M87 galaxy. These images were produced using 230 GHz observations performed in 2017 April. Additional observations are required to investigate the persistence of the primary image feature-a ring with azimuthal brightness asymmetry-and to quantify the image variability on event horizon scales. To address this need, we analyze M87* data collected with prototype EHT arrays in 2009, 2011, 2012, and 2013. While these observations do not contain enough information to produce images, they are sufficient to constrain simple geometric models. We develop a modeling approach based on the framework utilized for the 2017 EHT data analysis and validate our procedures using synthetic data. Applying the same approach to the observational data sets, we find the M87* morphology in 2009-2017 to be consistent with a persistent asymmetric ring of similar to 40 mu as diameter. The position angle of the peak intensity varies in time. In particular, we find a significant difference between the position angle measured in 2013 and 2017. These variations are in broad agreement with predictions of a subset of general relativistic magnetohydrodynamic simulations. We show that quantifying the variability across multiple observational epochs has the potential to constrain the physical properties of the source, such as the accretion state or the black hole spin.
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| 2. |
- Arvizu, Dan, et al.
(författare)
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Summary for Policy Makers: Intergovernmental Panel on Climate Change Special Report Renewable Energy Sources (SRREN)
- 2011
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The Working Group III Special Report on Renewable Energy Sources and Climate Change Mitigation (SRREN) presents an assessment of the literature on the scientific, technological, environmental, economic and social aspects of the contribution of six renewable energy (RE) sources to the mitigation of climate change. It is intended to provide policy relevant information to governments, intergovernmental processes and other interested parties. This Summary for Policymakers provides an overview of the SRREN, summarizing the essential findings. The SRREN consists of 11 chapters. Chapter 1 sets the context for RE and climate change; Chapters 2 through 7 provide information on six RE technologies, and Chapters 8 through 11 address integrative issues.
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| 3. |
- Arvizu, Dan, et al.
(författare)
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Technical Summary
- 2011
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Ingår i: IPCC Special Report on Renewable Energy Sources and Climate Change Mitigation.
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Bokkapitel (refereegranskat)
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| 4. |
- Bhalla, Aditya, et al.
(författare)
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Effective alkaline metal-catalyzed oxidative delignification of hybrid poplar
- 2016
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Ingår i: Biotechnology for Biofuels. - : Springer Science and Business Media LLC. - 1754-6834. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- BackgroundStrategies to improve copper-catalyzed alkaline hydrogen peroxide (Cu-AHP) pretreatment of hybrid poplar were investigated. These improvements included a combination of increasing hydrolysis yields, while simultaneously decreasing process inputs through (i) more efficient utilization of H2O2 and (ii) the addition of an alkaline extraction step prior to the metal-catalyzed AHP pretreatment. We hypothesized that utilizing this improved process could substantially lower the chemical inputs needed during pretreatment.ResultsHybrid poplar was pretreated utilizing a modified process in which an alkaline extraction step was incorporated prior to the Cu-AHP treatment step and H2O2 was added batch-wise over the course of 10 h. Our results revealed that the alkaline pre-extraction step improved both lignin and xylan solubilization, which ultimately led to improved glucose (86 %) and xylose (95 %) yields following enzymatic hydrolysis. An increase in the lignin solubilization was also observed with fed-batch H2O2 addition relative to batch-only addition, which again resulted in increased glucose and xylose yields (77 and 93 % versus 63 and 74 %, respectively). Importantly, combining these strategies led to significantly improved sugar yields (96 % glucose and 94 % xylose) following enzymatic hydrolysis. In addition, we found that we could substantially lower the chemical inputs (enzyme, H2O2, and catalyst), while still maintaining high product yields utilizing the improved Cu-AHP process. This pretreatment also provided a relatively pure lignin stream consisting of ≥90 % Klason lignin and only 3 % xylan and 2 % ash following precipitation. Two-dimensional heteronuclear single-quantum coherence (2D HSQC) NMR and size-exclusion chromatography demonstrated that the solubilized lignin was high molecular weight (Mw ≈ 22,000 Da) and only slightly oxidized relative to lignin from untreated poplar.ConclusionsThis study demonstrated that the fed-batch, two-stage Cu-AHP pretreatment process was effective in pretreating hybrid poplar for its conversion into fermentable sugars. Results showed sugar yields near the theoretical maximum were achieved from enzymatically hydrolyzed hybrid poplar by incorporating an alkaline extraction step prior to pretreatment and by efficiently utilizing H2O2 during the Cu-AHP process. Significantly, this study reports high sugar yields from woody biomass treated with an AHP pretreatment under mild reaction conditions.
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| 5. |
- Lu, R.S., et al.
(författare)
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A ring-like accretion structure in M87 connecting its black hole and jet
- 2023
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Ingår i: Nature. - 0028-0836 .- 1476-4687. ; 616:7958, s. 686-690
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Tidskriftsartikel (refereegranskat)abstract
- The nearby radio galaxy M87 is a prime target for studying black hole accretion and jet formation1,2. Event Horizon Telescope observations of M87 in 2017, at a wavelength of 1.3 mm, revealed a ring-like structure, which was interpreted as gravitationally lensed emission around a central black hole3. Here we report images of M87 obtained in 2018, at a wavelength of 3.5 mm, showing that the compact radio core is spatially resolved. High-resolution imaging shows a ring-like structure of [Formula: see text] Schwarzschild radii in diameter, approximately 50% larger than that seen at 1.3 mm. The outer edge at 3.5 mm is also larger than that at 1.3 mm. This larger and thicker ring indicates a substantial contribution from the accretion flow with absorption effects, in addition to the gravitationally lensed ring-like emission. The images show that the edge-brightened jet connects to the accretion flow of the black hole. Close to the black hole, the emission profile of the jet-launching region is wider than the expected profile of a black-hole-driven jet, suggesting the possible presence of a wind associated with the accretion flow.
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| 6. |
- Paulsson, Alexander, 1980-, et al.
(författare)
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Förändrade förutsättningar för framtidens kollektivtrafik : Trender och mottrender
- 2016
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Rapporten syftar till att, utifrån befintlig forskning, identifiera trender och mottrender som kan komma att påverka kollektivtrafiken på medellång och lång sikt. Analysen har genomförts utifrån sex olika områden som identifierats i samarbete med Trafikförvaltningen vid Stockholms läns landsting. I rapporten konstateras att globala krafter påverkar kollektivtrafiken på flera sätt, genom framväxten av en global marknad för kollektivtrafikaktörer och genom demografiska och ekonomiska förändringar som förändrar behovet av kollektivtrafik. Demografiska förändringar medför att Sverige befolkning antar en delvis ny skepnad med en växande befolkning och med fortsatt stark dragningskraft till storstadsregionerna. Det finns osäkerheter kring hur eventuella beteendeförändringar bland yngre befolkningsgrupper kommer att påverka transportsystemet. Fortsatt urbanisering, i världen men också i Sverige, ställer stora krav på att samordnad planering så att de möjligheter ökad koncentration gerkan tillvaratas och de negativa konsekvenserna kan mildras. Hållbarhetsbegreppet håller på att breddas till att, utöver miljö, i ökad utsträckning också inkludera ekonomiska och sociala dimensioner. Det påverkar synen på kollektivtrafikens roll för att uppnå hållbarhetsmål i samhället. Informationsteknikens utveckling i kombination med ambitioner att uppnå en mer hållbar mobilitet skapar drivkrafter för ett ökat fokus på hela resan, där nya mobilitetstjänster kan fungera som komplement eller supplement till kollektivtrafiken. I rapporten konstateras avslutningsvis att kraven på kostnadseffektivitet i offentlig verksamhet kommer att fortsätta forma hur kollektivtrafiken organiseras och styrs, men att det ännu är för tidigt att säga om någon ny, enhetlig modell ersätter New Public Management som dominerat inriktningen de senaste decennierna. Ökad samverkan på frivillig grund och mellan självständiga aktörer kommer sannolikt vara centralt under överskådlig tid.
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| 7. |
- Santana, Felipe A., et al.
(författare)
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Final Targeting Strategy for the SDSS-IV APOGEE-2S Survey
- 2021
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Ingår i: Astronomical Journal. - : American Astronomical Society. - 1538-3881 .- 0004-6256. ; 162:6
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Tidskriftsartikel (refereegranskat)abstract
- APOGEE is a high-resolution (R similar to 22,000), near-infrared, multi-epoch, spectroscopic survey of the Milky Way. The second generation of the APOGEE project, APOGEE-2, includes an expansion of the survey to the Southern Hemisphere called APOGEE-2S. This expansion enabled APOGEE to perform a fully panoramic mapping of all of the main regions of the Milky Way; in particular, by operating in the H band, APOGEE is uniquely able to probe the dust-hidden inner regions of the Milky Way that are best accessed from the Southern Hemisphere. In this paper we present the targeting strategy of APOGEE-2S, with special attention to documenting modifications to the original, previously published plan. The motivation for these changes is explained as well as an assessment of their effectiveness in achieving their intended scientific objective. In anticipation of this being the last paper detailing APOGEE targeting, we present an accounting of all such information complete through the end of the APOGEE-2S project; this includes several main survey programs dedicated to exploration of major stellar populations and regions of the Milky Way, as well as a full list of programs contributing to the APOGEE database through allocations of observing time by the Chilean National Time Allocation Committee and the Carnegie Institution for Science. This work was presented along with a companion article, Beaton et al. (2021), presenting the final target selection strategy adopted for APOGEE-2 in the Northern Hemisphere.
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| 8. |
- Tisdale, John, et al.
(författare)
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A Multiple UAV System for Vision-Based Search and Localization
- 2008
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Ingår i: Proceedings of the '08 American Control Conference. - Linköping : IEEE. - 9781424420797 - 9781424420780 ; , s. 1985-1990
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Konferensbidrag (refereegranskat)abstract
- The contribution of this paper is an experimentally verified real-time algorithm for combined probabilistic search and track using multiple unmanned aerial vehicles (UAVs). Distributed data fusion provides a framework for multiple sensors to search for a target and accurately estimate its position. Vision based sensing is employed, using fixed downward-looking cameras. These sensors are modeled to include vehicle state uncertainty and produce an estimate update regardless of whether the target is detected in the frame or not. This allows for a single framework for searching or tracking, and requires non-linear representations of the target position probability density function (PDF) and the sensor model. While a grid-based system for Bayesian estimation was used for the flight demonstrations, the use of a particle filter solution has also been examined.Multi-aircraft flight experiments demonstrate vision-based localization of a stationary target with estimated error covariance on the order of meters. This capability for real-time distributed estimation will be a necessary component for future research in information-theoretic control.
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