| 481. |
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| 482. |
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| 483. |
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| 484. |
- Gustafsson, Mats, 1966-, et al.
(författare)
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Spatial and temporal patterns of chloride deposition in Southern Sweden
- 2000
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Ingår i: Water, Air and Soil Pollution. - : KLUWER ACADEMIC PUBL. - 0049-6979 .- 1573-2932. ; 124:3-4, s. 345-369
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Tidskriftsartikel (refereegranskat)abstract
- Monthly bulk deposition of chloride at 49 stations in Southern Sweden between 1989 and 1995 was used to produce quarterly and annual deposition maps through ordinary block kriging. Generally, deposition decreases from the west coast and eastward and displays a large annual variation, governed by the frequency and intensity of midlatitude cyclones. The 1st quarter dominates the temporal pattern all years except 1992. The 4th quarter is the second most important and the 2nd and 3rd quarters have generally low deposition. The spatial deposition maximum was often displaced from the west coast to the western fringe of the South Swedish highland, due to orographic enhancement of precipitation. On the western rise of the highland, deposition almost entirely co-variates with precipitation. On the west coast and in the eastern part of Southern Sweden, the temporal pattern is a more complex result of precipitation and frequency of strong westerlies. Comparing the quarterly total dataset with precipitation and frequency of westerly gales shows that both the 3rd and 4th quarters have higher mean precipitation than the 1st quarter, but lower deposition, while the second quarter has substantially lower precipitation but almost equal deposition to the 3rd quarter. The frequency of westerly gales shows a clearer, linear relationship to quarterly deposition. The 1st quarter has the highest variability in deposition and precipitation as well as in frequency of westerly gales. The importance of single highly salt laden cyclones to the annual deposition is obvious in the 1st quarter of 1993. Changes in cyclone activity due to climate change is therefore of vital importance for the chemical characteristics of the midlatitude atmosphere.
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| 485. |
- Gustafsson, Mats, et al.
(författare)
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State-space models and stored electromagnetic energy for antennas in dispersive and heterogeneous media
- 2017
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Accurate and efficient evaluation of the stored energy is essential for Q-factors, physical bounds, and antenna current optimization. Here, it is shown that the stored energy can be estimated from quadratic forms based on a state-space representation derived from the electric and magnetic field integral equations. The derived expressions are valid for small antennas embedded in temporally dispersive and inhomogeneous media. The quadratic forms also provide simple single frequency formulas for the corresponding Q-factors. Numerical examples comparing the different Q-factors are presented for dipole and meander line antennas in conductive, Debye, and Lorentz media for homogeneous and inhomogeneous media. The computed Q-factors are also verified with the Q-factor obtained from the stored energy in Brune synthesized circuit models.
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| 486. |
- Gustafsson, Mats, et al.
(författare)
-
State-space models and stored electromagnetic energy for antennas in dispersive and heterogeneous media
- 2017
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Ingår i: Radio Science. - 0048-6604. ; 52:11, s. 1325-1343
-
Tidskriftsartikel (refereegranskat)abstract
- Accurate and efficient evaluation of the stored energy is essential for Q factors, physical bounds, and antenna current optimization. Here it is shown that the stored energy can be estimated from quadratic forms based on a state-space representation derived from the electric and magnetic field integral equations. The derived expressions are valid for small antennas embedded in temporally dispersive and inhomogeneous media. The quadratic forms also provide simple single frequency formulas for the corresponding Q factors. Numerical examples comparing the different Q factors are presented for dipole and meander line antennas in conductive, Debye, and Lorentz media for homogeneous and inhomogeneous media. The computed Q factors are also verified with the Q factor obtained from the stored energy in Brune synthesized circuit models.
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| 487. |
- Gustafsson, Mats
(författare)
-
State-space models for stored energy and Q-factors
- 2016
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Ingår i: 2016 URSI International Symposium on Electromagnetic Theory, EMTS 2016. - 9781509025022 ; , s. 226-228
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Konferensbidrag (refereegranskat)abstract
- Q-factors are often used to quantify bandwidth performance of resonant structures. The Q-factor is defined as the quotient between the stored and dissipated energies. The time average dissipated energy is reformulated in the dissipated power and is well defined. The definition and evaluation of the stored energy is much more challenging and there are presently several proposals but none is applicable for general radiating system. The main challenge is to separate the radiated and stored parts of the total energy. In this paper, an alternative approach is proposed that is based on a state-space model of the antenna. The state-space model describes the internal states of the system and models the states that stores the energy. The state-space model is determined from the impedance matrix of the electric field integral equation. This provides a computationally efficient way to determine the stored energy that can be used in antenna current optimization. The state-space approach offers also new insight into the challenges to define the stored energy for electrically large objects.
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| 488. |
- Gustafsson, Mats, et al.
(författare)
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Stored electromagnetic energy and antenna Q
- 2015
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Ingår i: Progress In Electromagnetics Research. - 1070-4698 .- 1559-8985. ; 150, s. 13-27
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Tidskriftsartikel (refereegranskat)abstract
- Decomposition of the electromagnetic energy into its stored and radiated parts is instrumental in the evaluation of antenna Q and the corresponding fundamental limitations on antennas. This decomposition is not unique and there are several proposals in the literature. Here, it is shown that stored energy defined from the difference between the energy density and the far field energy equals the energy expressions proposed by Vandenbosch for many but not all cases. This also explains the observed cases with negative stored energy and suggests a possible remedy to them. The results are compared with the classical explicit expressions for spherical regions where the results only differ by the electrical size ka that is interpreted as the far-field energy in the interior of the sphere.
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| 489. |
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| 490. |
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