| 1. |
- Abadie, J., et al.
(författare)
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Implementation and testing of the first prompt search for gravitational wave transients with electromagnetic counterparts
- 2012
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Ingår i: Astronomy & Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 539
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Tidskriftsartikel (refereegranskat)abstract
- Aims. A transient astrophysical event observed in both gravitational wave (GW) and electromagnetic (EM) channels would yield rich scientific rewards. A first program initiating EM follow-ups to possible transient GW events has been developed and exercised by the LIGO and Virgo community in association with several partners. In this paper, we describe and evaluate the methods used to promptly identify and localize GW event candidates and to request images of targeted sky locations. Methods. During two observing periods (Dec. 17, 2009 to Jan. 8, 2010 and Sep. 2 to Oct. 20, 2010), a low-latency analysis pipeline was used to identify GW event candidates and to reconstruct maps of possible sky locations. A catalog of nearby galaxies and Milky Way globular clusters was used to select the most promising sky positions to be imaged, and this directional information was delivered to EM observatories with time lags of about thirty minutes. A Monte Carlo simulation has been used to evaluate the low-latency GW pipeline's ability to reconstruct source positions correctly. Results. For signals near the detection threshold, our low-latency algorithms often localized simulated GW burst signals to tens of square degrees, while neutron star/neutron star inspirals and neutron star/black hole inspirals were localized to a few hundred square degrees. Localization precision improves for moderately stronger signals. The correct sky location of signals well above threshold and originating from nearby galaxies may be observed with similar to 50% or better probability with a few pointings of wide-field telescopes.
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| 2. |
- Stappers, B. W., et al.
(författare)
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Observing pulsars and fast transients with LOFAR
- 2011
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 530
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Tidskriftsartikel (refereegranskat)abstract
- Low frequency radio waves, while challenging to observe, are a rich source of information about pulsars. The LOw Frequency ARray (LOFAR) is a new radio interferometer operating in the lowest 4 octaves of the ionospheric "radio window": 10-240 MHz, that will greatly facilitate observing pulsars at low radio frequencies. Through the huge collecting area, long baselines, and flexible digital hardware, it is expected that LOFAR will revolutionize radio astronomy at the lowest frequencies visible from Earth. LOFAR is a next-generation radio telescope and a pathfinder to the Square Kilometre Array (SKA), in that it incorporates advanced multi-beaming techniques between thousands of individual elements. We discuss the motivation for low-frequency pulsar observations in general and the potential of LOFAR in addressing these science goals. We present LOFAR as it is designed to perform high-time-resolution observations of pulsars and other fast transients, and outline the various relevant observing modes and data reduction pipelines that are already or will soon be implemented to facilitate these observations. A number of results obtained from commissioning observations are presented to demonstrate the exciting potential of the telescope. This paper outlines the case for low frequency pulsar observations and is also intended to serve as a reference for upcoming pulsar/fast transient science papers with LOFAR.
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| 3. |
- Larsson, Simon B., et al.
(författare)
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HBsAg quantification for identification of liver disease in chronic hepatitis B virus carriers
- 2014
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Ingår i: Liver International. - : Wiley. - 1478-3223. ; 34:7
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Tidskriftsartikel (refereegranskat)abstract
- Background & Aims: Quantification of hepatitis B surface antigen (HBsAg) has been proposed as a useful diagnostic marker for clinical staging (identification of inactive carrier state) and prognosis of chronic hepatitis B virus (HBV) infection. The aim of this study was to investigate the correlation between HBsAg levels in serum and histological liver damage in patients with chronic infection. Methods: HBsAg levels in serum (by Abbott Architect) were related to HBV DNA, ALT and histological score (n = 160) and covalently closed circular DNA (cccDNA) (n = 84). Results: HBsAg levels correlated with cccDNA, serum HBV DNA, ALT and high inflammation scores (P < 0.001). Among HBeAg-negative patients, an HBsAg level below 3.0 log(10) IU/ml identified minimal liver damage (normal ALT and mild inflammation) with a predictive value of 92% (alone) or 96% (in combination with HBV DNA <4.0 log(10) copies/ml), whereas an HBsAg level above 3.5 log(10) IU/ml identified severe inflammation with a predictive value of 16% (alone) or 33% (in combination with HBV DNA >5.0 log(10) copies/ml). Conclusions: HBsAg levels reflect clinical stage and liver disease, and a combined quantification of HBsAg and HBV DNA may improve clinical staging.
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| 4. |
- Opgenoorth, Hermann J., et al.
(författare)
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Day-side ionospheric conductivities at Mars
- 2010
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Ingår i: Planetary and Space Science. - : Elsevier BV. - 0032-0633 .- 1873-5088. ; 58:10, s. 1139-1151
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Tidskriftsartikel (refereegranskat)abstract
- We present estimates of the day-side ionospheric conductivities at Mars based on magnetic field measurements by Mars Global Surveyor (MGS) at altitudes down to similar to 100 km during aerobraking orbits early in the mission. At Mars, the so-called ionospheric dynamo region, where plasma/neutral collisions permit electric currents perpendicular to the magnetic field, lies between 100 and 250 km altitude. We find that the ionosphere is highly conductive in this region, as expected, with peak Pedersen and Hall conductivities of 0.1-1.5 S/m depending on the solar illumination and induced magnetospheric conditions. Furthermore, we find a consistent double peak pattern in the altitude profile of the day-side Pedersen conductivity, similar to that on Titan found by Rosenqvist et al. (2009). A high altitude peak, located between 180 and 200 km, is equivalent to the terrestrial peak in the lower F-layer. A second and typically much stronger layer of Pedersen conductivity is observed between 120 and 130 km, which is below the Hall conductivity peak at about 130-140 km. In this altitude region, MGS finds a sharp decrease in induced magnetic field strength at the inner magnetospheric boundary, while the day-side electron density is known to remain high as far down as 100 km. We find that such Titan-like behaviour of the Pedersen conductivity is only observed under regions of strongly draped magnetospheric field-lines, and negligible crustal magnetic anomalies below the spacecraft. Above regions of strong crustal magnetic anomalies, the Pedersen conductivity profile becomes more Earth-like with one strong Pedersen peak above the Hall conductivity peak. Here, both conductivities are 1-2 orders of magnitude smaller than the above only weakly magnetised crustal regions, depending on the strength of the crustal anomaly field at ionospheric altitudes. This nature of the Pedersen conductivity together with the structured distribution of crustal anomalies all over the planet should give rise to strong conductivity gradients around such anomalies. Day-side ionospheric conductivities on Mars (in regions away from the crustal magnetic anomalies) and Titan seem to behave in a very similar manner when horizontally draped magnetic field-lines partially magnetise a sunlit ionosphere. Therefore, it appears that a similar double peak structure of strong Pedersen conductivity could be a more general feature of non-magnetised bodies with ionised upper atmospheres, and thus should be expected to occur also at other non-magnetised terrestrial planets like Venus or other planetary bodies within the host planet magnetospheres.
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| 5. |
- Westin, Johan, 1965, et al.
(författare)
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Are FoxP3(+) cells involved in hyporesponsiveness to interferon/ribavirin therapy in chronic hepatitis C?
- 2011
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Ingår i: Journal of viral hepatitis. - : Wiley. - 1365-2893 .- 1352-0504. ; 18:2, s. 149-151
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Tidskriftsartikel (refereegranskat)abstract
- Summary. We aimed to clarify the role of liver-infiltrating FoxP3(+)T cells for the response to therapy in chronic hepatitis C. Liver biopsies from 52 patients were collected prior to the start of interferon/ribavirin treatment, and the kinetics of viral decay during treatment were compared in patients with high and low infiltration of FoxP3(+) cells. These groups did not differ with respect to the effectiveness of early viral clearance or the frequency of sustained viral response. Our data imply that FoxP3(+) cell-mediated immunosuppression is not a major mechanism of hyporesponsiveness to interferon-based therapy in chronic hepatitis C.
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