| 1. |
- Alef, Walter, et al.
(författare)
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Geodetic data analysis of VGOS experiments
- 2021
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Ingår i: 2021 34th General Assembly and Scientific Symposium of the International Union of Radio Science, URSI GASS 2021.
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Konferensbidrag (refereegranskat)abstract
- Very Long Baseline Interferometry (VLBI) serves as one of the common geodetic methods to define the global reference frames and monitor Earth's orientation variations. The technical upgrade of the VLBI method known as the VLBI Global Observing System (VGOS) includes a critical re-design of the observed frequencies from the dual band mode (S and X band, i.e. 2 GHz and 8 GHz) to observations in a broadband (2-14 GHz). Since 2019 the first VGOS experiments are available for the geodetic analysis in free access at the International VLBI service for Geodesy and Astrometry (IVS). Also regional-only subnetworks such as European VLBI stations have succeeded already in VGOS mode. Based on these brand-new observations we review the current geodetic data analysis workflow to build a bridge between geodetic observed delays derived from different bands.
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| 2. |
- Colomer Sanmartin, Francisco, 1966
(författare)
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High Resolution Studies of Circumstellar Masers
- 1996
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis describes in detail the observational procedures that we have followed and developed to analyze several research projects organized at Onsala since 1990 to study the regions of SiO maser emission at 43 GHz in the circumstellar envelopes of late-type stars with very high angular resolution. The compact nature of these SiO maser regions has been demonstrated in this work. In fact, we find that they are an order of magnitude smaller than previously reported. As a consequence, they can be studied with the available VLBI instruments. We have used the EVN and VLBA telescopes to produce images of the distribution of the SiO maser features in several sources, in particular R Cassiopeiae and VX Sagittarii. Through this work, we discuss in detail the procedures involved in all the project steps, from the scheduling of the observations to the calibration, imaging, and modelling of the source structure. We compare our results with those of other instruments at different frequencies for the same objects. This thesis also describes the analysis of observations of water masers at 22 GHz in several late-type stars using the VLA. The limited resolution of these observations made us develop a computer program, "FG3", that would search for the maser sources (blended spatially and in frequency) and extract them via 3D least squares fitting to Gaussian functions. This is, to our knowledge, a new approach in this kind of investigations. This program provides information of the source structure distribution and kinematics, and also measures parameters that are directly related with the physical conditions in the masing regions. In particular, we conclude by the study of the fitted maser linewidths that water masers in late-type stars are unsaturated. We are not able to reach a clear conclusion for the SiO masers in the supergiant star VX Sgr, but there are indications that they might be saturated.
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| 3. |
- García Espada, Susana, 1979, et al.
(författare)
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Application of ray-tracing through the high resolution numerical weather model HIRLAM applying the Conformal Theory of Refraction
- 2011
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Ingår i: Proceedings of the 20th Meeting of the European VLBI Group for Geodesy and Astrometry. - 1864-1113. ; , s. 133-137
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In space geodetic techniques like VLBI and GPS, accuracyis limited by atmospheric propagation effects by neutralatmosphere in the troposphere. In recent years numerical weather models (NWM) have been applied to improve mapping functions which are used for tropospheric delay modeling in VLBI and GPS data analyses. A troposphere correction model applying ray-tracing through the Limited Area numerical weather prediction (NWP) HIRLAM 3D-VAR model and applying the Conformal Theory of Refraction is developed. The advantages of HIRLAM model are the high spatial resolution (0.2◦x0.2◦) and the high temporal resolution in prediction mode (every 3 hours). The advantages of the Conformal Theory of Refraction (Moritz, 1967) is that the atmospheric propagation effects are evaluated along the line of sight and the known vacuum elevation angle is used so no iterative calculations are needed. When ray-tracing through HIRLAM profiles and calculating the slant delays using the Conformal Theory of Refraction, we include the effect of an inhomogeneous atmosphere in the slant delays values.
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| 4. |
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| 5. |
- García Espada, Susana, 1979, et al.
(författare)
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Simulations of Different Antenna Velocities in VLBI Networks
- 2009
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Ingår i: Proceedings of the 19th European VLBI for Geodesy and Astrometry Working Meeting, 24-25 March 2009, Bordeaux. ; , s. 169-172
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The new 40-m radiotelescope of the National Geographical Institute (IGN) in Yebes (code Ys) started to participate in IVS geodetic VLBI sessions in 2008. The azimuth and elevation slew velocities cause stress on the structure,and therefore has an impact on the expected life of the instrument; this calls for slow velocities and accelerations. However, high velocities are needed for better network geodetic results because, in principle, they allow more observations to be performed. In order to evaluate the optimum slew velocities for the new antenna,we used the scheduling software SKED and created schedules with different antenna velocities for Ys. We focussed on the two sessions EURO94 and R1331 and analyzed the scheduleswith SKED itself, and with the VLBI analysis software SOLVE, both with and without introducing simulated atmosphere and clock contributions. We found that the schedules with a fast Ys antenna (3◦/s in az. and el.) give slightly better results than the ones with a slow Ys antenna(1◦/s in az. and el.). For the studied EURO session the standard deviation of the estimated topocentric U-component for Yebes is similar for a fast and slow antenna. For the R1-experiment the standard deviations of all three topocentric station components improve for a fast antenna. The SKED-only results appear to be too optimistic, while the SOLVE results show more realistic estimates for the UEN components and sigmas. We found no significant difference in the UEN sigmas with or without introducing simulatedatmospheric and clock contributions, although the wrms fit becomes slightly worse.
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| 6. |
- García Espada, Susana, 1979, et al.
(författare)
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Space Geodesy at Yebes: Station Motion from VLBI and GPS
- 2008
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Ingår i: in Proceedings of the 5th IVS General Meeting "Measuring the future", eds A. Finkelstein, D. Behrend. - 9785020253322 ; , s. 93-97
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 7. |
- Perez-Gracia, Jose Luis, et al.
(författare)
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Strategies to design clinical studies to identify predictive biomarkers in cancer research
- 2017
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Ingår i: Cancer Treatment Reviews. - : Elsevier BV. - 0305-7372. ; 53, s. 79-97
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Forskningsöversikt (refereegranskat)abstract
- The discovery of reliable biomarkers to predict efficacy and toxicity of anticancer drugs remains one of the key challenges in cancer research. Despite its relevance, no efficient study designs to identify promising candidate biomarkers have been established. This has led to the proliferation of a myriad of exploratory studies using dissimilar strategies, most of which fail to identify any promising targets and are seldom validated. The lack of a proper methodology also determines that many anti-cancer drugs are developed below their potential, due to failure to identify predictive biomarkers. While some drugs will be systematically administered to many patients who will not benefit from them, leading to unnecessary toxicities and costs, others will never reach registration due to our inability to identify the specific patient population in which they are active. Despite these drawbacks, a limited number of outstanding predictive biomarkers have been successfully identified and validated, and have changed the standard practice of oncology. In this manuscript, a multidisciplinary panel reviews how those key biomarkers were identified and, based on those experiences, proposes a methodological framework—the DESIGN guidelines—to standardize the clinical design of biomarker identification studies and to develop future research in this pivotal field.
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