| 1. |
- de Graauw, Th., et al.
(författare)
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The Herschel-Heterodyne Instrument for the Far-Infrared (HIFI)
- 2010
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 518, s. L6-
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Tidskriftsartikel (refereegranskat)abstract
- Aims: This paper describes the Heterodyne Instrument for the Far-Infrared (HIFI) that was launched onboard ESA's Herschel Space Observatory in May 2009. Methods: The instrument is a set of 7 heterodyne receivers that are electronically tuneable, covering 480-1250 GHz with SIS mixers and the 1410-1910 GHz range with hot electron bolometer (HEB) mixers. The local oscillator (LO) subsystem comprises a Ka-band synthesizer followed by 14 chains of frequency multipliers and 2 chains for each frequency band. A pair of auto-correlators and a pair of acousto-optical spectrometers process the two IF signals from the dual-polarization, single-pixel front-ends to provide instantaneous frequency coverage of 2 × 4 GHz, with a set of resolutions (125 kHz to 1 MHz) that are better than 0.1 km s-1. Results: After a successful qualification and a pre-launch TB/TV test program, the flight instrument is now in-orbit and completed successfully the commissioning and performance verification phase. The in-orbit performance of the receivers matches the pre-launch sensitivities. We also report on the in-orbit performance of the receivers and some first results of HIFI's operations. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.
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| 2. |
- Gupta, H., et al.
(författare)
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Detection of OH+ and H2O+ towards Orion KL
- 2010
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 521, s. L47-
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Tidskriftsartikel (refereegranskat)abstract
- We report observations of the reactive molecular ions OH+, H2O+, and H3O+ towards Orion KL with Herschel/HIFI. All three N = 1-0 fine-structure transitions of OH+ at 909, 971, and 1033 GHz and both fine-structure components of the doublet ortho-H2O+ 111-000 transition at 1115 and 1139 GHz were detected; an upper limit was obtained for H3O+. OH+ and H2O+ are observed purely in absorption, showing a narrow component at the source velocity of 9 km s-1, and a broad blueshifted absorption similar to that reported recently for HF and para-H218O, and attributed to the low velocity outflow of Orion KL. We estimate column densities of OH+ and H2O+ for the 9 km s-1 component of 9 ± 3 × 1012 cm-2 and 7 ± 2 × 1012 cm-2, and those in the outflow of 1.9 ± 0.7 × 1013 cm-2 and 1.0 ± 0.3 × 1013 cm-2. Upper limits of 2.4 × 1012 cm-2 and 8.7 × 1012 cm-2 were derived for the column densities of ortho and para-H3O+ from transitions near 985 and 1657 GHz. The column densities of the three ions are up to an order of magnitude lower than those obtained from recent observations of W31C and W49N. The comparatively low column densities may be explained by a higher gas density despite the assumption of a very high ionization rate.
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| 3. |
- Lis, D. C., et al.
(författare)
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Herschel/HIFI measurements of the ortho/para ratio in water towards Sagittarius B2(M) and W31C
- 2010
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 521:1, s. Article Number: L26 -
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Tidskriftsartikel (refereegranskat)abstract
- We present Herschel/HIFI observations of the fundamental rotational transitions of ortho- and para-H216O and H218O in absorption towards Sagittarius B2(M) and W31C. The ortho/para ratio in water in the foreground clouds on the line of sight towards these bright continuum sources is generally consistent with the statistical high-temperature ratio of 3, within the observational uncertainties. However, somewhat unexpectedly, we derive a low ortho/para ratio of 2.35 +/- 0.35, corresponding to a spin temperature of similar to 27 K, towards Sagittarius B2(M) at velocities of the expanding molecular ring. Water molecules in this region appear to have formed with, or relaxed to, an ortho/para ratio close to the value corresponding to the local temperature of the gas and dust.
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| 4. |
- Roelfsema, P. R., et al.
(författare)
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In-orbit performance of Herschel-HIFI
- 2012
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 537
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Tidskriftsartikel (refereegranskat)abstract
- Aims: In this paper the calibration and in-orbit performance of the Heterodyne Instrument for the Far-Infrared (HIFI) is described.Methods: The calibration of HIFI is based on a combination of ground and in-flight tests. Dedicated ground tests to determine those instrument parameters that can only be measured accurately using controlled laboratory stimuli were carried out in the instrument level test (ILT) campaign. Special in-flight tests during the commissioning phase (CoP) and performance verification (PV) allowed the determination of the remaining instrument parameters. The various instrument observing modes, as specified in astronomical observation templates (AOTs), were validated in parallel during PV by observing selected celestial sources.Results: The initial calibration and in-orbit performance of HIFI has been established. A first estimate of the calibration budget is given. The overall in-flight instrument performance agrees with the original specification. Issues remain at only a few frequencies. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.
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| 5. |
- Shipman, R., et al.
(författare)
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Data processing pipeline for Herschel HIFI
- 2017
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 608, s. A49-
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Tidskriftsartikel (refereegranskat)abstract
- Context. The HIFI instrument on the Herschel Space Observatory performed over 9100 astronomical observations, almost 900 of which were calibration observations in the course of the nearly four-year Herschel mission. The data from each observation had to be converted from raw telemetry into calibrated products and were included in the Herschel Science Archive. Aims. The HIFI pipeline was designed to provide robust conversion from raw telemetry into calibrated data throughout all phases of the HIFI missions. Pre-launch laboratory testing was supported as were routine mission operations. Methods. A modular software design allowed components to be easily added, removed, amended and / or extended as the understanding of the HIFI data developed during and after mission operations. Results. The HIFI pipeline processed data from all HIFI observing modes within the Herschel automated processing environment as well as within an interactive environment. The same software can be used by the general astronomical community to reprocess any standard HIFI observation. The pipeline also recorded the consistency of processing results and provided automated quality reports. Many pipeline modules were in use since the HIFI pre-launch instrument level testing. Conclusions. Processing in steps facilitated data analysis to discover and address instrument artefacts and uncertainties. The availability of the same pipeline components from pre-launch throughout the mission made for well-understood, tested, and stable processing. A smooth transition from one phase to the next significantly enhanced processing reliability and robustness.
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| 6. |
- Dias, David O., et al.
(författare)
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Pericyte-derived fibrotic scarring is conserved across diverse central nervous system lesions
- 2021
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 12:1
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Tidskriftsartikel (refereegranskat)abstract
- Fibrotic scar tissue limits central nervous system regeneration in adult mammals. The extent of fibrotic tissue generation and distribution of stromal cells across different lesions in the brain and spinal cord has not been systematically investigated in mice and humans. Furthermore, it is unknown whether scar-forming stromal cells have the same origin throughout the central nervous system and in different types of lesions. In the current study, we compared fibrotic scarring in human pathological tissue and corresponding mouse models of penetrating and non-penetrating spinal cord injury, traumatic brain injury, ischemic stroke, multiple sclerosis and glioblastoma. We show that the extent and distribution of stromal cells are specific to the type of lesion and, in most cases, similar between mice and humans. Employing in vivo lineage tracing, we report that in all mouse models that develop fibrotic tissue, the primary source of scar-forming fibroblasts is a discrete subset of perivascular cells, termed type A pericytes. Perivascular cells with a type A pericyte marker profile also exist in the human brain and spinal cord. We uncover type A pericyte-derived fibrosis as a conserved mechanism that may be explored as a therapeutic target to improve recovery after central nervous system lesions.
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| 7. |
- Magnusson, Jens P, et al.
(författare)
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A latent neurogenic program in astrocytes regulated by Notch signaling in the mouse.
- 2014
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 1095-9203 .- 0036-8075. ; 346:6206, s. 237-241
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Tidskriftsartikel (refereegranskat)abstract
- Neurogenesis is restricted in the adult mammalian brain; most neurons are neither exchanged during normal life nor replaced in pathological situations. We report that stroke elicits a latent neurogenic program in striatal astrocytes in mice. Notch1 signaling is reduced in astrocytes after stroke, and attenuated Notch1 signaling is necessary for neurogenesis by striatal astrocytes. Blocking Notch signaling triggers astrocytes in the striatum and the medial cortex to enter a neurogenic program, even in the absence of stroke, resulting in 850 ± 210 (mean ± SEM) new neurons in a mouse striatum. Thus, under Notch signaling regulation, astrocytes in the adult mouse brain parenchyma carry a latent neurogenic program that may potentially be useful for neuronal replacement strategies.
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| 8. |
- Santopolo, Giuseppe, et al.
(författare)
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Blocking Notch-Signaling Increases Neurogenesis in the Striatum after Stroke
- 2020
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Ingår i: Cells. - : MDPI AG. - 2073-4409. ; 9:7
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Tidskriftsartikel (refereegranskat)abstract
- Stroke triggers neurogenesis in the striatum in mice, with new neurons deriving in part from the nearby subventricular zone and in part from parenchymal astrocytes. The initiation of neurogenesis by astrocytes within the striatum is triggered by reduced Notch-signaling, and blocking this signaling pathway by deletion of the gene encoding the obligate Notch coactivator Rbpj is sufficient to activate neurogenesis by striatal astrocytes in the absence of an injury. Here we report that blocking Notch-signaling in stroke increases the neurogenic response to stroke 3.5-fold in mice. Deletion of Rbpj results in the recruitment of a larger number of parenchymal astrocytes to neurogenesis and over larger areas of the striatum. These data suggest inhibition of Notch-signaling as a potential translational strategy to promote neuronal regeneration after stroke.
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| 9. |
- Säwen, Petter, et al.
(författare)
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Murine HSCs contribute actively to native hematopoiesis but with reduced differentiation capacity upon aging
- 2018
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Ingår i: Elife. - 2050-084X. ; 7
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Tidskriftsartikel (refereegranskat)abstract
- A hallmark of adult hematopoiesis is the continuous replacement of blood cells with limited lifespans. While active hematopoietic stem cell (HSC) contribution to multilineage hematopoiesis is the foundation of clinical HSC transplantation, recent reports have questioned the physiological contribution of HSCs to normal/steady-state adult hematopoiesis. Here, we use inducible lineage tracing from genetically marked adult HSCs and reveal robust HSC-derived multilineage hematopoiesis. This commences via defined progenitor cells, but varies substantially in between different hematopoietic lineages. By contrast, adult HSC contribution to hematopoietic cells with proposed fetal origins is neglible. Finally, we establish that the HSC contribution to multilineage hematopoiesis declines with increasing age. Therefore, while HSCs are active contributors to native adult hematopoiesis, it appears that the numerical increase of HSCs is a physiologically relevant compensatory mechanism to account for their reduced differentiation capacity with age.
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