| 1. |
- Andersson, Martin, et al.
(författare)
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HYPERFINE-DEPENDENT gf -VALUES OF Mn i LINES IN THE 1.49–1.80 μm H BAND
- 2015
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Ingår i: The Astrophysical Journal Supplement Series. - : American Astronomical Society. - 0067-0049 .- 1538-4365. ; 216:1
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Tidskriftsartikel (refereegranskat)abstract
- The three Mn I lines at 17325, 17339, and 17349 angstrom are among the 25 strongest lines (log(gf) > 0.5) in the H band. They are all heavily broadened due to hyperfine structure, and the profiles of these lines have so far not been understood. Earlier studies of these lines even suggested that they were blended. In this work, the profiles of these three infrared (IR) lines have been studied theoretically and compared to experimental spectra to assist in the complete understanding of the solar spectrum in the IR. It is shown that the structure of these lines cannot be described in the conventional way using the diagonal A and B hyperfine interaction constants. The off-diagonal hyperfine interaction not only has a large impact on the energies of the hyperfine levels, but also introduces a large intensity redistribution among the hyperfine lines, changing the line profiles dramatically. By performing large-scale calculations of the diagonal and off-diagonal hyperfine interaction and the gf-values between the upper and lower hyperfine levels and using a semi-empirical fitting procedure, we achieved agreement between our synthetic and experimental spectra. Furthermore, we compare our results with observations of stellar spectra. The spectra of the Sun and the K1.5 III red giant star Arcturus were modeled in the relevant region, 1.73-1.74 mu m, using our theoretically predicted gf-values and energies for each individual hyperfine line. Satisfactory fits were obtained and clear improvements were found using our new data compared with the old available Mn I data. A complete list of energies and gf-values for all the 3d(5)4s(S-7)4d e(6)D - 3d(5)4s(S-7)4f w(6)F hyperfine lines are available as supporting material, whereas only the stronger lines are presented and discussed in detail in this paper.
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| 2. |
- Aourir, Nouria, et al.
(författare)
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Theoretical hyperfine structures of F-19 I and O-17 I
- 2018
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Ingår i: Physical Review A: covering atomic, molecular, and optical physics and quantum information. - : American Physical Society. - 2469-9926 .- 2469-9934. ; 97:3
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Tidskriftsartikel (refereegranskat)abstract
- Multiconfiguration Hartree-Fock (MCHF) and multiconfiguration Dirac-Hartree-Fock (MCDHF) calculations are performed for the 2p(5) P-2 degrees, 2p(4)(P-3)3s P-4, 2p(4)(P-3)3s P-2, and 2p(4)(P-3)3 p S-4 degrees states of F-19 I to determine their hyperfine constants. Several computing strategies are considered to investigate electron correlation and relativistic effects. High-order correlation contributions are included in MCHF calculations based on single and double multireference expansions. The largest components of the single reference MCHF wave functions are selected to define the multireference (MR) sets. In this scheme, relativistic corrections are evaluated in the Breit-Pauli approximation. A similar strategy is used for the calculation of MCDHF relativistic wave functions and hyperfine parameters. While correlation and relativistic corrections are found to be rather small for the ground state, we highlight large relativistic effects on the hyperfine constant A(3/2) of 2p(4)(P-3)3 p(4)S(degrees) and, to a lesser extent, on A(1/2) of 2p(4)(P-3)3s P-4. As expected for such a light system, electron correlation effects dominate over relativity in the calculation of the hyperfine interaction of all other levels considered. We also revisit the hyperfine constants of 2p(3)((4)(S))3s S-5 degrees and 2p(3)(S-4)3 p P-5 in O-17 using similar strategies. The results are found to be in excellent agreement with experiment.
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| 3. |
- Atalay, B., et al.
(författare)
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MCDHF and RCI calculations of energy levels, lifetimes, and transition rates in Si III and Si IV
- 2019
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 631
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Tidskriftsartikel (refereegranskat)abstract
- We present extensive multiconfiguration Dirac-Hartree-Fock and relativistic configuration interaction calculations including 106 states in doubly ionized silicon (Si III) and 45 states in triply ionized silicon (Si IV), which are important for astrophysical determination of plasma properties in different objects. These calculations represents an important extension and improvement of earlier calculations especially for Si III. The calculations are in good agreement with available experiments for excitation energies, transition properties, and lifetimes. Important deviations from the NIST-database for a selection of perturbed Rydberg series are discussed in detail.
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| 4. |
- Bieron, Jacek, et al.
(författare)
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Ab initio calculations of the hyperfine structure of zinc and evaluation of the nuclear quadrupole moment Q(Zn-67)
- 2018
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Ingår i: Physical Review A: covering atomic, molecular, and optical physics and quantum information. - : American Physical Society. - 2469-9926 .- 2469-9934. ; 97:6
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Tidskriftsartikel (refereegranskat)abstract
- The relativistic multiconfiguration Dirac-Hartree-Fock and the nonrelativistic multiconfiguration Hartree-Fock methods have been employed to calculate the magnetic dipole and electric quadrupole hyperfine structure constants of zinc. The calculated electric field gradients for the 4s4p P-3(1)degrees and 4s4p P-3(2)degrees states, together with experimental values of the electric quadrupole hyperfine structure constants, made it possible to extract a nuclear electric quadrupole moment Q((67) Zn) = 0.122(10) b. The error bar was evaluated in a quasistatistical approach-the calculations were carried out with 11 different methods, and then the error bar was estimated from the differences between the results obtained with those methods.
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| 5. |
- Bieron, Jacek, et al.
(författare)
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Ab initio MCDHF calculations of electron-nucleus interactions
- 2015
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Ingår i: Physica Scripta. - : Institute of Physics Publishing (IOPP). - 0031-8949 .- 1402-4896. ; 90:5
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Tidskriftsartikel (refereegranskat)abstract
- We present recent advances in the development of atomic ab initio multiconfiguration Dirac– Hartree–Fock theory, implemented in the GRASP relativistic atomic structure code. For neutral atoms, the deviations of properties calculated within the Dirac–Hartree–Fock (DHF) method (based on independent particle model of an atomic cloud) are usually dominated by electron correlation effects, i.e. the non-central interactions of individual electrons. We present the recent advances in accurate calculations of electron correlation effects in small, medium, and heavy neutral atoms. We describe methods of systematic development of multiconfiguration expansions leading to systematic, controlled improvement of the accuracy of the ab initio calculations. These methods originate from the concept of the complete active space (CAS) model within the DHF theory, which, at least in principle, permits fully relativistic calculations with full account of electron correlation effects. The calculations within the CAS model on currently available computer systems are feasible only for very light systems. For heavier atoms or ions with more than a few electrons, restrictions have to be imposed on the multiconfiguration expansions. We present methods and tools, which are designed to extend the numerical calculations in a controlled manner, where multiconfiguration expansions account for all leading electron correlation effects. We show examples of applications of the GRASP code to calculations of hyperfine structure constants, but the code may be used for calculations of arbitrary bound-state atomic properties. In recent years it has been applied to calculations of atomic and ionic spectra (transition energies and rates), to determinations of nuclear electromagnetic moments, as well as to calculations related to interactions of bound electrons with nuclear electromagnetic moments leading to violations of discrete symmetries.
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| 6. |
- Cai, Zhanzhang, et al.
(författare)
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Performance of Smoothing Methods for Reconstructing NDVI Time-Series and Estimating Vegetation Phenology from MODIS Data
- 2017
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Ingår i: Remote Sensing. - : MDPI. - 2072-4292. ; 9:12
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Tidskriftsartikel (refereegranskat)abstract
- Many time-series smoothing methods can be used for reducing noise and extracting plant phenological parameters from remotely-sensed data, but there is still no conclusive evidence in favor of one method over others. Here we use moderate-resolution imaging spectroradiometer (MODIS) derived normalized difference vegetation index (NDVI) to investigate five smoothing methods: Savitzky-Golay fitting (SG), locally weighted regression scatterplot smoothing (LO), spline smoothing (SP), asymmetric Gaussian function fitting (AG), and double logistic function fitting (DL). We use ground tower measured NDVI (10 sites) and gross primary productivity (GPP, 4 sites) to evaluate the smoothed satellite-derived NDVI time-series, and elevation data to evaluate phenology parameters derived from smoothed NDVI. The results indicate that all smoothing methods can reduce noise and improve signal quality, but that no single method always performs better than others. Overall, the local filtering methods (SG and LO) can generate very accurate results if smoothing parameters are optimally calibrated. If local calibration cannot be performed, cross validation is a way to automatically determine the smoothing parameter. However, this method may in some cases generate poor fits, and when calibration is not possible the function fitting methods (AG and DL) provide the most robust description of the seasonal dynamics.
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| 7. |
- Eklundh, Lars, et al.
(författare)
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TIMESAT : A Software Package for Time-Series Processing and Assessment of Vegetation Dynamics
- 2015
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Ingår i: Remote Sensing Time Series. - Cham : Springer. - 9783319159676 - 9783319159669 ; 22, s. 141-158
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Large volumes of data from satellite sensors with high time-resolution 6 exist today, e.g. Advanced Very High Resolution Radiometer (AVHRR) and 7 Moderate Resolution Imaging Spectroradiometer (MODIS), calling for efficient 8 data processing methods. TIMESAT is a free software package for processing 9 satellite time-series data in order to investigate problems related to global change 10 and monitoring of vegetation resources. The assumptions behind TIMESAT are 11 that the sensor data represent the seasonal vegetation signal in a meaningful way, 12 and that the underlying vegetation variation is smooth. A number of processing 13 steps are taken to transform the noisy signals into smooth seasonal curves, including 14 fitting asymmetric Gaussian or logistic functions, or smoothing the data using a 15 modified Savitzky-Golay filter. TIMESAT can adapt to the upper envelope of the 16 data, accounting for negatively biased noise, and can take missing data and quality 17 flags into account. The software enables the extraction of seasonality parameters, 18 like the beginning and end of the growing season, its length, integrated values, etc. 19 TIMESAT has been used in a large number of applied studies for phenology 20 parameter extraction, data smoothing, and general data quality improvement. To 21 enable efficient analysis of future Earth Observation data sets, developments of 22 TIMESAT are directed towards processing of high-spatial resolution data from 23 e.g. Landsat and Sentinel-2, and use of spatio-temporal data processing methods.
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| 8. |
- Eklundh, Lars, et al.
(författare)
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Timesat for processing time-series data from satellite sensors for land surface monitoring
- 2016
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Ingår i: Remote Sensing and Digital Image Processing. - Cham : Springer International Publishing. - 2215-1842 .- 1567-3200. - 9783319470351 - 9783319470375 ; 20, s. 177-194
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Bokkapitel (refereegranskat)abstract
- The TIMESAT software package has been developed to enable monitoring of dynamic land surface processes using remotely sensed data. The monitoring capability is based on processing of time-series for each image pixel using either of three smoothing methods included in TIMESAT: asymmetric Gaussian fits, doublelogistic fits, and Savitzky-Golay filtering. The methods have different properties and are suitable for a wide range of data with different character and noise properties. The fitting methods can be upper-envelope weighted and can take quality data into account. Based on the fitted functions, growing season parameters are then extracted (beginning, end, amplitude, slope, integral, etc.), and can be merged into images. TIMESAT has been used in a number of application fields: mapping of phenology and phenological variations; ecological disturbances; vegetation classification and characterization; agriculture applications; climate applications; and for improving remote sensing signal quality. Future developments of TIMESAT will include new methods to better handle long gaps in time-series, handling of irregular time sampling, improved smoothing methods, and incorporation of the spatial domain. These modifications will enable use of TIMESAT also for high-resolution data, e.g. data from the planned ESA Sentinel-2 satellite.
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| 9. |
- Ekman, Jörgen, et al.
(författare)
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Large-scale calculations of atomic level and transition properties in the aluminum isoelectronic sequence from Ti X through Kr XXIV, Xe XLII, and W LXII
- 2018
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Ingår i: Atomic Data and Nuclear Data Tables. - : Elsevier. - 0092-640X .- 1090-2090. ; 120, s. 152-262
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Tidskriftsartikel (refereegranskat)abstract
- Large-scale self-consistent multiconfiguration Dirac-Hartree-Fock subsequent relativistic configuration interaction (RCl) calculations are reported for 360 states belonging to the 30 configurations 3s(2))3l, 4l. 5l}, 3p(2) (3d, 4l}, 3s(3p(2). 3d(2)),3s{3p3d, 3p4l. 3p5s, 3d4l'}, 3p3d(2), 3p(3) and 3d(3) with I = 0, 1,, n - 1 and l' = 0. 1. 2 in 17 systems of the aluminum-like isoelectronic sequence: Ti X through Kr XXIV, Xe XLII, and W LXII. Effects from electron correlation are taken into account by means of large expansions in terms of a basis of configuration state functions (CSF) and calculated energy levels are compared with existing theoretical calculations and the NIST Atomic Spectra database. Radiative E1, E2, M1 and M2 transition rates and associated lifetimes of energy levels are presented in online tables. The uncertainties of the calculated energies are very small, on average between 0.02% and 0.05%, which aid new line identifications in laboratory and astronomical spectra and also make it possible to find and rule out misidentifications. The uncertainties of the El transition probabilities, based on the agreement between values in the length and velocity gauges, are estimated to be of the order 0.5% for the strong transitions and 25% for the weaker intercombination transitions. The M1 transition values are not sensitive to electron correlation and are believed to be accurate to well within 1%. (C) 2017 Published by Elsevier Inc.
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| 10. |
- Ekman, Jörgen, et al.
(författare)
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RIS4 : A program for relativistic isotope shift calculations
- 2019
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Ingår i: Computer Physics Communications. - : Elsevier. - 0010-4655 .- 1879-2944. ; 235, s. 433-446
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Tidskriftsartikel (refereegranskat)abstract
- Spectral lines from different isotopes display a small separation in energy, commonly referred to as the line isotope shift. The program RIS4 (Relativistic Isotope Shift) calculates normal and specific mass shift parameters as well as field shift electronic factors from relativistic multiconfiguration Dirac-Hartree-Fock wave functions. These quantities, together with available nuclear data, determine isotope-dependent energy shifts. Using a reformulation of the field shift, it is possible to study, in a model-independent way, the atomic energy shifts arising from changes in nuclear charge distributions, e.g. deformations. (C) 2018 Published by Elsevier B.V.
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