| 1. |
- Abelev, Betty, et al.
(författare)
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Long-range angular correlations on the near and away side in p-Pb collisions at root S-NN=5.02 TeV
- 2013
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Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 719:1-3, s. 29-41
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Tidskriftsartikel (refereegranskat)abstract
- Angular correlations between charged trigger and associated particles are measured by the ALICE detector in p-Pb collisions at a nucleon-nucleon centre-of-mass energy of 5.02 TeV for transverse momentum ranges within 0.5 < P-T,P-assoc < P-T,P-trig < 4 GeV/c. The correlations are measured over two units of pseudorapidity and full azimuthal angle in different intervals of event multiplicity, and expressed as associated yield per trigger particle. Two long-range ridge-like structures, one on the near side and one on the away side, are observed when the per-trigger yield obtained in low-multiplicity events is subtracted from the one in high-multiplicity events. The excess on the near-side is qualitatively similar to that recently reported by the CMS Collaboration, while the excess on the away-side is reported for the first time. The two-ridge structure projected onto azimuthal angle is quantified with the second and third Fourier coefficients as well as by near-side and away-side yields and widths. The yields on the near side and on the away side are equal within the uncertainties for all studied event multiplicity and p(T) bins, and the widths show no significant evolution with event multiplicity or p(T). These findings suggest that the near-side ridge is accompanied by an essentially identical away-side ridge. (c) 2013 CERN. Published by Elsevier B.V. All rights reserved.
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| 2. |
- Albentosa, Ezequiel, et al.
(författare)
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Current Status of the EU-VGOS Project
- 2023
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Ingår i: International VLBI Service for Geodesy and Astrometry 2022 General Meeting Proceedings. ; NASA/ CP–20220018789, s. 85-89
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Konferensbidrag (refereegranskat)abstract
- The EU-VGOS project began in 2018 with the aim of using the VGOS infrastructure in Europe to investigate methods for VGOS data processing. The project is now structured into Working Groups dealing with operations (stations), e-transfer, correlation and post-processing, and analysis. This is a report on the status of the project.
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| 3. |
- 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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| 4. |
- Alef, Walter, et al.
(författare)
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The EUropean-VGOS Project
- 2019
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Ingår i: Proceedings of the 24th European VLBI Group for Geodesy and Astrometry Working Meeting. - 9788441656345 ; , s. 107-111
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Konferensbidrag (refereegranskat)abstract
- In Spring 2018 the Bonn correlation centre started a collaboration with the three European stations of Wettzell, Onsala and Yebes, equipped with both S/X- and broadband systems, to perform VGOS-like test sessions. The aim is to verify and develop further the processing chain for VGOS experiments end-to-end, from the scheduling to the analysis of the derived observables. We will present the current status of the project.
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| 5. |
- Baranov, Viktor, et al.
(författare)
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Complex and nonlinear climate-driven changes in freshwater insect communities over 42 years
- 2020
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Ingår i: Conservation Biology. - : John Wiley & Sons. - 0888-8892 .- 1523-1739. ; 34:5, s. 1241-1251
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Tidskriftsartikel (refereegranskat)abstract
- The ongoing biodiversity crisis becomes evident in the widely observed decline in abundance and diversity of species, profound changes in community structure, and shifts in species' phenology. Insects are among the most affected groups, with documented decreases in abundance up to 76% in the last 25–30 years in some terrestrial ecosystems. Identifying the underlying drivers is a major obstacle as most ecosystems are affected by multiple stressors simultaneously and in situ measurements of environmental variables are often missing. In our study, we investigated a headwater stream belonging to the most common stream type in Germany located in a nature reserve with no major anthropogenic impacts except climate change. We used the most comprehensive quantitative long‐term data set on aquatic insects available, which includes weekly measurements of species‐level insect abundance, daily water temperature and stream discharge as well as measurements of additional physicochemical variables for a 42‐year period (1969–2010). Overall, water temperature increased by 1.88°C and discharge patterns changed significantly. These changes were accompanied by an 81.6% decline in insect abundance, but an increase in richness (+8.5%), Shannon diversity (+22.7%), evenness (+22.4%), and interannual turnover (+34%). Moreover, the community's trophic structure and phenology changed: the duration of emergence increased by 15.2 days, whereas the peak of emergence moved 13.4 days earlier. Additionally, we observed short‐term fluctuations (<5 years) in almost all metrics as well as complex and nonlinear responses of the community toward climate change that would have been missed by simply using snapshot data or shorter time series. Our results indicate that climate change has already altered biotic communities severely even in protected areas, where no other interacting stressors (pollution, habitat fragmentation, etc.) are present. This is a striking example of the scientific value of comprehensive long‐term data in capturing the complex responses of communities toward climate change.
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| 6. |
- Calves, G. M., et al.
(författare)
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Observations and analysis of phase scintillation of spacecraft signal on the interplanetary plasma
- 2014
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 564
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Tidskriftsartikel (refereegranskat)abstract
- Aims. The phase scintillation of the European Space Agency's Venus Express (VEX) spacecraft telemetry signal was observed at X-band (lambda = 3.6 cm) with a number of radio telescopes of the European Very Long Baseline Interferometry (VLBI) Network in the period 2009-2013. Methods. We found a phase fluctuation spectrum along the Venus orbit with a nearly constant spectral index of -2.42 +/- 0.25 over the full range of solar elongation angles from 0 degrees to 45 degrees, which is consistent with Kolmogorov turbulence. Radio astronomical observations of spacecraft signals within the solar system give a unique opportunity to study the temporal behaviour of the signal's phase fluctuations caused by its propagation through the interplanetary plasma and the Earth's ionosphere. This gives complementary data to the classical interplanetary scintillation (IPS) study based on observations of the flux variability of distant natural radio sources. Results. We present here our technique and the results on IPS. We compare these with the total electron content for the line of sight through the solar wind. Finally, we evaluate the applicability of the presented technique to phase-referencing VLBI and Doppler observations of currently operational and prospective space missions.
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| 7. |
- Dorigo, Wouter, et al.
(författare)
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The International Soil Moisture Network : Serving Earth system science for over a decade
- 2021
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Ingår i: Hydrology and Earth System Sciences. - : Copernicus GmbH. - 1027-5606 .- 1607-7938. ; 25:11, s. 5749-5804
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Forskningsöversikt (refereegranskat)abstract
- In 2009, the International Soil Moisture Network (ISMN) was initiated as a community effort, funded by the European Space Agency, to serve as a centralised data hosting facility for globally available in situ soil moisture measurements . The ISMN brings together in situ soil moisture measurements collected and freely shared by a multitude of organisations, harmonises them in terms of units and sampling rates, applies advanced quality control, and stores them in a database. Users can freely retrieve the data from this database through an online web portal (https://ismn.earth/en/, last access: 28 October 2021). Meanwhile, the ISMN has evolved into the primary in situ soil moisture reference database worldwide, as evidenced by more than 3000 active users and over 1000 scientific publications referencing the data sets provided by the network. As of July 2021, the ISMN now contains the data of 71 networks and 2842 stations located all over the globe, with a time period spanning from 1952 to the present. The number of networks and stations covered by the ISMN is still growing, and approximately 70 % of the data sets contained in the database continue to be updated on a regular or irregular basis. The main scope of this paper is to inform readers about the evolution of the ISMN over the past decade, including a description of network and data set updates and quality control procedures. A comprehensive review of the existing literature making use of ISMN data is also provided in order to identify current limitations in functionality and data usage and to shape priorities for the next decade of operations of this unique community-based data repository.
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| 8. |
- Haas, Rüdiger, 1966, et al.
(författare)
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Near real-time monitoring of UT1 with geodetic VLBI
- 2011
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Ingår i: Proceedings of the 20th Meeting of the European VLBI Group for Geodesy and Astrometry. - 1864-1113. ; , s. 64-66
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- We give a short overview on the current status of near real-time monitoring of UT1 with geodetic VLBI. The use ofreal-time data transfer together with automated correlation and data analysis makes it possible to derive final dUT1-results with very low latency. The agreement with IERS C04 results is on the level of 30 msec. It is even possible to determine time series of dUT1 during ongoing 24 h IVS-sessions. The concept is highly relevant for future VLBI2010 operations.
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| 9. |
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| 10. |
- Haas, Rüdiger, 1966, et al.
(författare)
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Ultra-Rapid DUT1-Observations with E-VLBI
- 2010
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Ingår i: Artificial Satellites. - : Walter de Gruyter GmbH. - 0208-841X .- 2083-6104. ; 45:2 / 2010, s. 75-79
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Konferensbidrag (refereegranskat)abstract
- We give a short overview about the achievements of the Fennoscandian- Japanese ultra-rapid dUT1-project that was initiated in early 2007. The combination of real-time data transfer, near real-time data conversion and correlation, together with near-real time data analysis allows to determine dUT1 with a very low latency of less than 5 minutes after the end of a VLBI-session. The accuracy of these ultra-rapid dUT1-results is on the same order than the results of the standard rapid-service of the International Earth Rotation and Reference Frame Service (IERS). The ultra-rapid approach is currently extended to 24 hour sessions and is expected to become an important contribution for the future next generation VLBI system called VLBI2010.
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| 11. |
- Koyama, Yasuhiro, et al.
(författare)
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Ultra rapid dUT1 estimations from e-VLBI sessions
- 2010
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Ingår i: Advances in Geosciences: Volume 20: Solid Earth (SE); World Scientific Publishing Company. - : World Scientific Publishing Company. - 9789812838186 ; 20, s. 197-204
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Konferensbidrag (refereegranskat)abstract
- Promptness of the data processing of the international VLBI observations has been continuously improved in the past decades. In particular, e-VLBI technique has proved that it has a capability to shorten the latency by transferring the observed data to the correlator by using high speed communication networks. The method has been introduced to routine intensive VLBI sessions to monitor dUT1. To improve the promptness even further, we started an initiative to develop automated data transfer and data processing systems using Europe-Japan baselines. On February 21, 2008, we succeeded to demonstrate the effectiveness of the developed systems and estimated the dUT1 parameter 3 minutes 45 seconds after the last scan of the one hour intensive style e-VLBI session. This achievement was realized by the developments of the K5/VSSP32 data acquisition terminal, automated data processing and analysis software.
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| 12. |
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| 13. |
- Roy, Alan, et al.
(författare)
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VLBI at APEX: First Fringes
- 2012
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Ingår i: Proceedings of Science. - 1824-8039. ; 2012-October
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Konferensbidrag (refereegranskat)
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| 14. |
- Schmidt, Rüdiger, et al.
(författare)
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Sputter Yield Amplification of reactively sputtered TiO2
- 2011
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Konferensbidrag (refereegranskat)abstract
- TiO2 is a material with attractive properties which have led to various applications such as anti-reflective coatings [1] or self cleaning surfaces [2]. One of the most applied deposition techniques used for TiO2 is reactive magnetron sputtering. Unfortunately TiO2 suffers from a comparatively low deposition rate when reactively sputtered. To increase the deposition rate, Sputter Yield Amplification (SYA) can be used through recoil of the sputtering species at implanted heavy dopants below the target surface [3,4]. Here we present experimental results showing a large increase of the TiO2 deposition rate when doped with Tungsten. Although SYA has been proposed earlier [5], the production of doped targets was complicated. We have built a designated sputter deposition tool which enables systematic studies of SYA. In this study the rate increase by SYA is investigated for two different dopants, namely Tungsten and Bismuth. Bismuth was chosen since it is the heaviest non-radioactive material available. Our experiments show that the rate increase of TiO2 by Bismuth is surprisingly low. Tungsten on the other hand results in a large rate increase of 160% in DC and 220% in HiPIMS mode. A number of additional experiments have been carried out to verify and explain this observation. Finally TRIDYN [6] simulations have been performed which reproduce the experimental results.
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| 15. |
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| 16. |
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| 17. |
- Tuccari, Gino, et al.
(författare)
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DBBC3 — The new wide-band backend for VLBI
- 2018
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Ingår i: Proceedings of Science. - 1824-8039. ; 344
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Konferensbidrag (refereegranskat)abstract
- The DBBC3 VLBI digital backend is the successor of the most widely adapted digital VLBI backend DBBC2. The DBBC3 offers much wider bandwidth and integrated Ethernet output. Three different firmwares for observing have been implemented until now: Direct Sampling Conversion (DSC), arbitrary selection of bands (OCT), and Digital Down Conversion (DDC). These modes cover all the requirements of the astronomical, VGOS and legacy geodetic VLBI of today, but also of the near future. In addition the DBBC3 offers unsurpassed compatibility to the relatively large number of other existing VLBI backends. A number of DBBC3 systems have been deployed and more are currently under construction, with the number of 4 GHz bands ranging from 2 up to 8 with resulting typical output data-rates from 32 Gbps to 128 Gbps. Laboratory and field tests have been performed.
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| 18. |
- Tuccari, Gino, et al.
(författare)
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DBBC3 Towards the BRAND EVN Receiver
- 2019
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Ingår i: Proceedings of the 24th European VLBI Group for Geodesy and Astrometry Working Meeting. ; , s. 27-30
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Konferensbidrag (refereegranskat)abstract
- The DBBC3 is a flexible VLBI backend and environment that supports a wide range of observational needs via a suite of FPGA firmware types. The hardware can sample up to eight 4 GHz-wide baseband signals and convert to digital streams over multiple 10GE links on fibre. The development team has an ongoing development programme that has enhanced existing modes and introduced new desired modes as user requirements evolve. Three dierent firmware types for observing have been implemented which will be briefly summarised: Direct Sampling Conversion (DSC), arbitrary selection of bands (OCT), Digital Down Conversion (DDC). These modes cover all the requirements of astronomical, VGOS and legacy geodetic VLBI of the present, but also of the near future. At the same time the DBBC3 is an important platform for additional new modes to be implemented for the BRAND receiver. This paper describes the use of the DBBC3 for the receiver development, pointing out which element in the current DBBC3 structure will be part of the BRAND receiver in order to simplify its introduction into the existing VLBI environment at telescopes with a DBBC3 backend.
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| 19. |
- Wagner, J., et al.
(författare)
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First 230? : GHz VLBI fringes on 3C 279 using the APEX Telescope (Research Note)
- 2015
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 581
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Tidskriftsartikel (refereegranskat)abstract
- Aims. We report about a 230? GHz very long baseline interferometry (VLBI) fringe finder observation of blazar 3C 279 with the APEX telescope in Chile, the phased submillimeter array (SMA), and the SMT of the Arizona Radio Observatory (ARO). Methods. We installed VLBI equipment and measured the APEX station position to 1? cm accuracy (1σ). We then observed 3C 279 on 2012 May 7 in a 5? h 230? GHz VLBI track with baseline lengths of 2800? Mλ to 7200? Mλ and a finest fringe spacing of 28.6? μas. Results. Fringes were detected on all baselines with signal-to-noise ratios of 12 to 55 in 420? s. The correlated flux density on the longest baseline was ∼0.3? Jy beam-1, out of a total flux density of 19.8? Jy. Visibility data suggest an emission region ≤ 38? μas in size, and at least two components, possibly polarized. We find a lower limit of the brightness temperature of the inner jet region of about 1010? K. Lastly, we find an upper limit of 20% on the linear polarization fraction at a fringe spacing of ∼ 38? μas. Conclusions. With APEX the angular resolution of 230? GHz VLBI improves to 28.6? μas. This allows one to resolve the last-photon ring around the Galactic Center black hole event horizon, expected to be 40? μas in diameter, and probe radio jet launching at unprecedented resolution, down to a few gravitational radii in galaxies like M 87. To probe the structure in the inner parsecs of 3C 279 in detail, follow-up observations with APEX and five other mm-VLBI stations have been conducted (March 2013) and are being analyzed.
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