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- Heald, G. H., et al.
(författare)
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The LOFAR Multifrequency Snapshot Sky Survey (MSSS) : I. Survey description and first results
- 2015
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 582, s. 1-22
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Tidskriftsartikel (refereegranskat)abstract
- We present the Multifrequency Snapshot Sky Survey (MSSS), the first northern-sky Low Frequency Array (LOFAR) imaging survey. In this introductory paper, we first describe in detail the motivation and design of the survey. Compared to previous radio surveys, MSSS is exceptional due to its intrinsic multifrequency nature providing information about the spectral properties of the detected sources over more than two octaves (from 30 to 160 MHz). The broadband frequency coverage, together with the fast survey speed generated by LOFAR’s multibeaming capabilities, make MSSS the first survey of the sort anticipated to be carried out with the forthcoming Square Kilometre Array (SKA). Two of the sixteen frequency bands included in the survey were chosen to exactly overlap the frequency coverage of large-area Very Large Array (VLA) and Giant Metrewave Radio Telescope (GMRT) surveys at 74 MHz and 151 MHz respectively. The survey performance is illustrated within the MSSS Verification Field (MVF), a region of 100 square degrees centered at (α,δ)J2000 = (15h,69°). The MSSS results from the MVF are compared with previous radio survey catalogs. We assess the flux and astrometric uncertainties in the catalog, as well as the completeness and reliability considering our source finding strategy. We determine the 90% completeness levels within the MVF to be 100 mJy at 135 MHz with 108″ resolution, and 550 mJy at 50 MHz with 166″ resolution. Images and catalogs for the full survey, expected to contain 150 000–200 000 sources, will be released to a public web server. We outline the plans for the ongoing production of the final survey products, and the ultimate public release of images and source catalogs.
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2. |
- Orrù, E., et al.
(författare)
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Wide-field LOFAR imaging of the field around the double-double radio galaxy B1834+620 : A fresh view on a restarted AGN and doubeltjes
- 2015
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 584, s. 1-12
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Tidskriftsartikel (refereegranskat)abstract
- Context. The existence of double-double radio galaxies (DDRGs) is evidence for recurrent jet activity in active galactic nuclei (AGN), as expected from standard accretion models. A detailed study of these rare sources provides new perspectives for investigating the AGN duty cycle, AGN-galaxy feedback, and accretion mechanisms. Large catalogues of radio sources, on the other hand, provide statistical information about the evolution of the radio-loud AGN population out to high redshifts.Aims. Using wide-field imaging with the LOFAR telescope, we study both a well-known DDRG as well as a large number of radio sources in the field of view.Methods. We present a high resolution image of the DDRG B1834+620 obtained at 144 MHz using LOFAR commissioning data. Our image covers about 100 square degrees and contains over 1000 sources.Results. The four components of the DDRG B1834+620 have been resolved for the first time at 144 MHz. Inner lobes were found to point towards the direction of the outer lobes, unlike standard FR II sources. Polarized emission was detected at +60 rad m-2 in the northern outer lobe. The high spatial resolution allows the identification of a large number of small double-lobed radio sources; roughly 10% of all sources in the field are doubles with a separation smaller than 1′.Conclusions. The spectral fit of the four components is consistent with a scenario in which the outer lobes are still active or the jets recently switched off, while emission of the inner lobes is the result of a mix-up of new and old jet activity. From the presence of the newly extended features in the inner lobes of the DDRG, we can infer that the mechanism responsible for their formation is the bow shock that is driven by the newly launched jet. We find that the density of the small doubles exceeds the density of FR II sources with similar properties at 1.4 GHz, but this difference becomes smaller for low flux densities. Finally, we show that the significant challenges of wide-field imaging (e.g., time and frequency variation of the beam, directional dependent calibration errors) can be solved using LOFAR commissioning data, thus demonstrating the potential of the full LOFAR telescope to discover millions of powerful AGN at redshift z ~ 1.
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3. |
- Nooijen, C. F., et al.
(författare)
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Working mechanisms of a behavioural intervention promoting physical activity in persons with subacute spinal cord injury
- 2016
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Ingår i: Journal of Rehabilitation Medicine. - : Medical Journals Sweden AB. - 1650-1977 .- 1651-2081. ; 48:7, s. 583-8
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVE: In order to unravel the working mechanisms that underlie the effectiveness of a behavioural intervention promoting physical activity in persons with subacute spinal cord injury, the aim of this study was to assess the mediating effects of physical and psychosocial factors on the intervention effect on physical activity. DESIGN: Randomized controlled trial. SETTING: Four rehabilitation centres in the Netherlands. SUBJECTS: Thirty-nine persons with subacute spinal cord injury. INTERVENTION: Behavioural intervention promoting an active lifestyle, based on motivational interviewing. The intervention involved a total of 13 individual sessions beginning 2 months before and ending 6 months after discharge from initial inpatient rehabilitation. MAIN MEASURES: The potential mediating effects of fatigue, pain, depression, illness cognition, exercise self-efficacy, coping and social support on the effect of the behavioural intervention on objectively measured physical activity (B = 0.35 h, p < 0.01) were studied. Measurements were performed at baseline, discharge, 6 months and 1 year after discharge. RESULTS: No single factor was found that strongly mediated the effect of the behavioural intervention on physical activity; however, multiple factors could partly explain the effect. Mediating effects greater than 10% were found for proactive coping (17.6%), exercise self-efficacy (15.9%), pain disability (15.3%) and helplessness (12.5%). DISCUSSION: Proactive coping (the ability to anticipate and deal with potential threats before they occur), exercise self-efficacy (self-confidence with respect to performing exercise and daily physical activities), pain disability (interference by pain of daily activities) and helplessness (emphasizing the aversive meaning of the disease) are important concepts in interventions promoting physical activity in persons with subacute spinal cord injury.
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4. |
- Bärebring, Linnea, et al.
(författare)
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Preeclampsia and Blood Pressure Trajectory during Pregnancy in Relation to Vitamin D Status
- 2016
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Ingår i: Plos One. - : Public Library of Science (PLoS). - 1932-6203. ; 11:3
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Tidskriftsartikel (refereegranskat)abstract
- Every tenth pregnancy is affected by hypertension, one of the most common complications and leading causes of maternal death worldwide. Hypertensive disorders in pregnancy include pregnancy-induced hypertension and preeclampsia. The pathophysiology of the development of hypertension in pregnancy is unknown, but studies suggest an association with vitamin D status, measured as 25-hydroxyvitamin D (25(OH) D). The aim of this study was to investigate the association between gestational 25(OH) D concentration and preeclampsia, pregnancy-induced hypertension and blood pressure trajectory. This cohort study included 2000 women. Blood was collected at the first (T1) and third (T3) trimester (mean gestational weeks 10.8 and 33.4). Blood pressure at gestational weeks 10, 25, 32 and 37 as well as symptoms of preeclampsia and pregnancy-induced hypertension were retrieved from medical records. Serum 25(OH) D concentrations (LC-MS/MS) in T1 was not significantly associated with preeclampsia. However, both 25(OH) D in T3 and change in 25 (OH) D from T1 to T3 were significantly and negatively associated with preeclampsia. Women with a change in 25(OH) D concentration of >= 30 nmol/L had an odds ratio of 0.22 (p = 0.002) for preeclampsia. T1 25(OH) D was positively related to T1 systolic (beta = 0.03, p = 0.022) and T1 diastolic blood pressure (beta = 0.02, p = 0.016), and to systolic (beta = 0.02, p = 0.02) blood pressure trajectory during pregnancy, in adjusted analyses. There was no association between 25(OH) D and pregnancy-induced hypertension in adjusted analysis. In conclusion, an increase in 25(OH) D concentration during pregnancy of at least 30 nmol/L, regardless of vitamin D status in T1, was associated with a lower odds ratio for preeclampsia. Vitamin D status was significantly and positively associated with T1 blood pressure and gestational systolic blood pressure trajectory but not with pregnancy-induced hypertension.
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5. |
- Bärebring, Linnea, et al.
(författare)
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Trajectory of vitamin D status during pregnancy in relation to neonatal birth size and fetal survival: a prospective cohort study
- 2018
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Ingår i: BMC Pregnancy and Childbirth. - : Springer Science and Business Media LLC. - 1471-2393. ; 18
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Tidskriftsartikel (refereegranskat)abstract
- Background: We investigated the associations between vitamin D status in early and late pregnancy with neonatal small for gestational age (SGA), low birth weight (LBW) and preterm delivery. Furthermore, associations between vitamin D status and pregnancy loss were studied. Methods: Serum 25-hydroxyvitamin D (25OHD) was sampled in gestational week <= 16 (trimester 1 (T1), N = 2046) and > 31 (trimester 3 (T3), N = 1816) and analysed using liquid chromatography tandem mass spectrometry. Pregnant women were recruited at antenatal clinics in south-west Sweden at latitude 57-58 degrees N. Gestational and neonatal data were retrieved from medical records. Multiple gestations and terminated pregnancies were excluded from the analyses. SGA was defined as weight and/or length at birth < 2 SD of the population mean and LBW as < 2500 g. Preterm delivery was defined as delivery < 37 + 0 gestational weeks and pregnancy loss as spontaneous abortion or intrauterine fetal death. Associations between neonatal outcomes and 25OHD at T1, T3 and change in 25OHD (T3-T1) were studied using logistic regression. Results: T1 25OHD was negatively associated with pregnancy loss and 1 nmol/L increase in 25OHD was associated with 1% lower odds of pregnancy loss (OR 0.99, p = 0.046). T3 25OHD >= 100 nmol/L (equal to 40 ng/ml) was associated with lower odds of SGA (OR 0.3, p = 0.031) and LBW (OR 0.2, p = 0.046), compared to vitamin D deficiency (25OHD < 30 nmol/L, or 12 ng/ml). Women with a >= 30 nmol/L increment in 25OHD from T1 to T3 had the lowest odds of SGA, LBW and preterm delivery. Conclusions: Vitamin D deficiency in late pregnancy was associated with higher odds of SGA and LBW. Lower 25OHD in early pregnancy was only associated with pregnancy loss. Vitamin D status trajectory from early to late pregnancy was inversely associated with SGA, LBW and preterm delivery with the lowest odds among women with the highest increment in 25OHD. Thus, both higher vitamin D status in late pregnancy and gestational vitamin D status trajectory can be suspected to play a role in healthy pregnancy.
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