| 1. |
- Gruber, T, et al.
(författare)
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Geodetic SAR for Height System Unification and Sea Level Research - Observation Concept and Results in the Baltic Sea
- 2021
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Konferensbidrag (refereegranskat)abstract
- Traditionally, sea level is observed at tide gauge stations, which usually also serve as height reference stations for national leveling networks and therefore define a height system of a country. Thus, sea level research across countries is closely linked to height system unification and needs to be regarded jointly. One of the main deficiencies to use tide gauge data for geodetic sea level research and height systems unification is that only a few stations are connected to permanent GNSS receivers next to the tide gauge in order to systematically observe vertical land motion. As a new observation technique, absolute positioning by SAR using active transponders on ground can fill this gap by systematically observing time series of geometric heights at tide gauge stations. By additionally knowing the tide gauge geoid heights in a global height reference frame, one can finally obtain absolute sea level heights at each tide gauge. With this information the impact of climate change on the sea level can be quantified in an absolute manner and height systems can be connected across the oceans. First results from applying this technique at selected tide gauges at the Baltic coasts are promising but also exhibit some problems related to the new technique. The paper presents the concept of using the new observation type in an integrated sea level observing system and provides results for a test network in the Baltic sea area by combining geometric and physical heights with tide gauge readings.
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| 2. |
- Andersson, Pontus, 1971, et al.
(författare)
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Radiative lifetimes of metastable states of negative ions
- 2006
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622 .- 2469-9926 .- 2469-9934. ; 73, s. 032705-
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Tidskriftsartikel (refereegranskat)abstract
- We present a technique for measuring the radiative lifetimes of metastable states of negative ions that involves the use of a heavy-ion storage ring. The method has been applied to investigate the radiative decay of the np(3) P-2(1/2) levels of Te-(n=5) and Se-(n=4) and the 3p(3) D-2 state of Si- for which the J=3/2 and 5/2 levels were unresolved. All of these states are metastable and decay primarily by emission of E2 and M1 radiation. Multi Configuration Dirac-Hartree-Fock calculations of rates for the transitions in Te- and Se- yielded lifetimes of 0.45 s and 4.7 s, respectively. The measured values agree well with these predicted values. In the case of the D-2 state of Si-, however, our measurement was only able to set a lower limit on the lifetime. The upper limit of the lifetime that can be measured with our apparatus is set by how long the ions can be stored in the ring, a limit determined by the rate of collisional detachment. Our lower limit of 1 min for the lifetime of the D-2 state is consistent with both the calculated lifetimes of 162 s for the D-2(3/2) level and 27.3 h for the D-2(5/2) level reported by O'Malley and Beck and 14.5 h and 12.5 h, respectively, from our Breit-Pauli calculations.
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| 3. |
- Ellmann, A, et al.
(författare)
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Radiative lifetime of a bound excited state of Te-
- 2004
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 92:25, s. 253002-
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Tidskriftsartikel (refereegranskat)abstract
- We report on the first experimental study of the lifetime of a bound excited state of a negative ion. A new experimental technique was developed and used to measure the radiative lifetime of the 5p(5) P-2(1/2) level of Te-. The experiment was performed in a magnetic storage ring, where a laser beam was applied along one of the straight sections. In the experiment the population of the excited J=1/2 level was probed each time the Te- ions passed through the laser field. A decay curve was built up by sampling the population of the excited level of the Te- ions as a function of time after injection into the ring. A multiconfiguration Dirac-Hartree-Fock calculation was performed in conjunction with the experiment. The calculation yielded a radiative lifetime of 0.45 s, in excellent agreement with the measured value of 0.42(5) s.
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| 4. |
- Abbak, Ramazan A., et al.
(författare)
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A precise gravimetric geoid model in a mountainous area with scarce gravity data : a case study in central Turkey
- 2012
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Ingår i: Studia Geophysica et Geodaetica. - : Springer Science and Business Media LLC. - 0039-3169 .- 1573-1626. ; 56:4, s. 909-927
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Tidskriftsartikel (refereegranskat)abstract
- In mountainous regions with scarce gravity data, gravimetric geoid determination is a difficult task that needs special attention to obtain reliable results satisfying the demands, e.g., of engineering applications. The present study investigates a procedure for combining a suitable global geopotential model and available terrestrial data in order to obtain a precise regional geoid model for Konya Closed Basin (KCB). The KCB is located in the central part of Turkey, where a very limited amount of terrestrial gravity data is available. Various data sources, such as the Turkish digital elevation model with 3 '' x 3 '' resolution, a recently published satellite-only global geopotential model from the Gravity Recovery and Climate Experiment satellite (GRACE) and the ground gravity observations, are combined in the least-squares sense by the modified Stokes' formula. The new gravimetric geoid model is compared with Global Positioning System (GPS)/levelling at the control points, resulting in the Root Mean Square Error (RMS) differences of +/- 6.4 cm and 1.7 ppm in the absolute and relative senses, respectively. This regional geoid model appears to he more accurate than the Earth Gravitational Model 2008, which is the best global model over the target area, with the RMS differences of +/- 8.6 cm and 1.8 ppm in the absolute and relative senses, respectively. These results show that the accuracy of a regional gravimetric model can be augmented by the combination of a global geopotential model and local terrestrial data in mountainous areas even though the quality and resolution of the primary terrestrial data are not satisfactory to the geoid modelling procedure.
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| 5. |
- Biémont, E, et al.
(författare)
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Decay of metastable states in Nd II
- 2007
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Ingår i: The European physical journal D Atomic, molecular and optical physics. ; 41, s. 211-
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Tidskriftsartikel (refereegranskat)
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| 6. |
- Biémont, É., et al.
(författare)
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Decay of metastable states in NdII
- 2007
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Ingår i: European Physical Journal D. - : Springer Science and Business Media LLC. - 1434-6060 .- 1434-6079. ; 41:2, s. 211-219
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Tidskriftsartikel (refereegranskat)abstract
- The difficulty associated with an accurate determination of transition rates for forbidden lines in lowly ionized heavy elements is illustrated in the case of Nd II. We have investigated the radiative decay of the low-lying metastable levels in Nd+ including the two levels 4f(4)(I-5) 5d K-6(11/2) and 4f(4)(I-5) 5d I-6(13/2). In these two particular cases, using di. erent theoretical approaches, we. nd that the decay is dominated by the M1 channels but that the E2 contributions are of the same order of magnitude. These levels have also been studied experimentally by lifetime measurements with the heavy ion storage ring CRYRING of Stockholm University. The difficulties encountered when performing such experiments are underlined and discussed.
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| 7. |
- Hartman, Henrik, et al.
(författare)
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The FERRUM project : experimentally determined metastable lifetimes and transition probabilities for forbidden [Ti II] lines observed in eta Carinae
- 2005
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 361:1, s. 206-210
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Tidskriftsartikel (refereegranskat)abstract
- In the spectrum of an emission-line region ejected from the massive star Eta Carinae, called the strontium filament (SrF), forbidden lines from many elements, in particular [Sr II] and [Ti II], are observed. These lines are strong in this specific region and valuable for plasma diagnostics. Forbidden lines are not easily produced in laboratory light sources and the atomic parameters for these lines can thus not be measured in a straightforward way. We use a combination of laboratory and astrophysical measurements to determine transition probabilities for the [Ti II] lines. Lifetimes for metastable levels in Ti II are measured using a laser probing technique on a stored ion beam at CRYRING, MSL, Stockholm. Branching fractions from some of these levels are derived from Hubble Space Telescope/STIS spectra of the SrF. The astrophysical branching fractions are combined with the experimental lifetimes to determine absolute transition probabilities. We report lifetimes for the Ti II levels b(4)P(3/2), b(2)P(1/2), c(2)D(3/2) and c(2)D(5/2), in the range 0.29-17 s, and transition probabilities for eight parity-forbidden lines from the levels c(2)D(3/2) and c(2)D(5/2), along with uncertainty estimates.
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| 8. |
- Mannervik, S, et al.
(författare)
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Lifetime measurements by laser probing in CRYRING - Recent experimental developments
- 2005
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Ingår i: Physica Scripta. - 0031-8949 .- 1402-4896. ; T119, s. 49-54
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Tidskriftsartikel (refereegranskat)abstract
- A laser probing technique for lifetime measurements of long- lived metastable levels has been developed at the ion storage ring CRYRING. The method has been in use for about eight years and it has been applied to various ions. Levels with radiative lifetimes from a few milliseconds up to 28 s have been measured. The method has been continuously developed and this article is focused on recent experimental developments of the method in order to widen its applicability and to increase its efficiency and accuracy.
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