| 1. |
- Burmeister, F., et al.
(författare)
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A study of the inner-valence ionization region in HCl and DCl
- 2004
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Ingår i: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 37:6, s. 1173-1183
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Tidskriftsartikel (refereegranskat)abstract
- An in-depth photoionization study of the inner-valence electrons in HCl and DCl has been performed using synchrotron radiation. A series of photoelectron spectra of HCl were obtained at a resolution of 23 meV over the binding energy range 25-30.5 eV at various excitation energies and at two different electron collection angles relative to the plane of polarization of the undulator radiation. In addition, photoelectron spectra of DCl were recorded at two different excitation energies. These spectra were compared directly with the threshold photoelectron spectra of HCl and DCl that were recorded previously under similar resolution conditions (similar to30 meV). This comparative study reveals new information on the nature of the numerous band systems observed in this binding energy region. In addition, we present the experimental confirmation of the theoretical prediction given by Andersson et al (2001 Phys. Rev. A 65 012705) that a vibrational progression showing interference structure would appear in the main inner-valence ionization band in the photoelectron spectrum of DCl at a resolution of 10 meV.
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| 2. |
- Andersson, L. Mauritz, et al.
(författare)
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Nonadiabatic effects in the photoelectron spectra of HCl and DCl. II. Theory
- 2002
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 65:1
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Tidskriftsartikel (refereegranskat)abstract
- The vibrationally resolved photoelectron spectra of HCl and DCl in the 25-28 eV region were computed using a time-dependent approach for the nuclear dynamics. The spectral features cannot be understood without including a nonadiabatic coupling between the dissociative 3 (2)Sigma(+) state and the bound 4 (2)Sigma(+) state in the adiabatic picture. Alternatively, in the diabatic picture a dissociative two-hole-one-particle state interacts with a bound one-hole state. The molecular system is of intermediate coupling strength, i.e., it cannot be described by a single potential-energy curve. The interaction between a bound and a dissociative state leads to Fano resonances superimposed on a broad back-round, as observed in the experimental spectra [Burmeister et al., Phys. Rev. A 65, 012704 (2001)]. From modified potential-energy curves, all features of the experimental spectra, including Fano resonance parameters and lifetimes, were reproduced. From the simulations we observe that two additional peaks in the experimental DCl spectra should appear if the resolution were to be enhanced to around 10 meV.
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| 3. |
- Andersson, L. Mauritz, et al.
(författare)
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Properties of a discretized coherent state representation and the relation to Gabor analysis
- 2002
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Ingår i: Journal of Physics A. - : IOP Publishing. - 0305-4470 .- 1361-6447. ; 35:36, s. 7787-7801
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Tidskriftsartikel (refereegranskat)abstract
- Properties of a discretized coherent state representation (DCSR) and its connection to Gabor frame analysis are discussed. The DCSR approach was recently shown (Andersson L M 2001 J. Chem. Phys. 115 1158) to yield a practical computational scheme for quantum dynamics, and an iterative scheme for finding the identity operator was proposed. In the present work, we suggest a proof of fast convergence of the iterative scheme for computing the canonical dual to any given countable frame in a Hilbert space. The method of frames is concerned with the use of a non-orthogonal, over-complete set of functions for expansion of an arbitrary function. We also introduce the concept of 'representations of the identity operator' and show how to expand arbitrary vectors using the frame elements, without explicit diagonalization to an orthonormal basis. Numerical examples that illustrate the method are shown.
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| 4. |
- Collins, C. G., et al.
(författare)
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Experimental warming differentially affects vegetative and reproductive phenology of tundra plants
- 2021
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 12:1
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Tidskriftsartikel (refereegranskat)abstract
- Rapid climate warming is altering Arctic and alpine tundra ecosystem structure and function, including shifts in plant phenology. While the advancement of green up and flowering are well-documented, it remains unclear whether all phenophases, particularly those later in the season, will shift in unison or respond divergently to warming. Here, we present the largest synthesis to our knowledge of experimental warming effects on tundra plant phenology from the International Tundra Experiment. We examine the effect of warming on a suite of season-wide plant phenophases. Results challenge the expectation that all phenophases will advance in unison to warming. Instead, we find that experimental warming caused: (1) larger phenological shifts in reproductive versus vegetative phenophases and (2) advanced reproductive phenophases and green up but delayed leaf senescence which translated to a lengthening of the growing season by approximately 3%. Patterns were consistent across sites, plant species and over time. The advancement of reproductive seasons and lengthening of growing seasons may have significant consequences for trophic interactions and ecosystem function across the tundra. It is unclear whether climate driven phenological shifts of tundra plants are consistent across the plant growing season. Here the authors analyse data from a network of field warming experiments in Arctic and alpine tundra, finding that warming differentially affects the timing and duration of reproductive and vegetative phenology.
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| 5. |
- Ekenberg, Ulf, et al.
(författare)
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Control of spontaneous spin splitting in an asymmetric quantum well with the use of strain and/or magnetic field
- 2001
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Ingår i: Physica. E, Low-Dimensional systems and nanostructures. - 1386-9477 .- 1873-1759. ; 10:03-jan, s. 81-85
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Tidskriftsartikel (refereegranskat)abstract
- Spin-orbit coupling combined with inversion asymmetry gives rise to spin splitting even in the absence of an applied magnetic field. The size of this spin splitting can be controlled by changing the degree of asymmetry using a gate voltage. We present here other less obvious ways of controlling the spontaneous spin splitting in a two-dimensional hole gas, where these effects are particularly large. Applying moderate stress can easily decrease the spin splitting by an order of magnitude. The mechanism is the strain-induced energy shift of the heavy-hole and light-hole subbands, which diminishes the degree of band mixing, which is found to be strongly correlated to the spin splitting. An applied magnetic field causes an additional Zeeman splitting, but we find that a magnetic field of 1T can be sufficient to practically erase the difference between a symmetric quantum well (without subband splitting) and an asymmetric quantum well. We have simulated Shubnikov-de Haas oscillations and found that two periodicities in 1/B can occur even for one filled spin-degenerate hole subband.
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| 6. |
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| 7. |
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| 8. |
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| 9. |
- Mauritz, O., et al.
(författare)
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Magnetic-field-induced suppression of spontaneous spin-splitting of hole subbands
- 2000
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Ingår i: Physica. E, Low-Dimensional systems and nanostructures. - 1386-9477 .- 1873-1759. ; 6:04-jan, s. 779-782
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Tidskriftsartikel (refereegranskat)abstract
- The spin-splitting in the valence band in an InxGa1-xAs/InxGa1-xAsyP1-y quantum well is investigated theoretically using a 6 x 6 Luttinger-Kohn Hamiltonian. We compare the Landau levels in a perpendicular magnetic field with the corresponding results for the subband dispersion;. It is shown that the asymmetry of the quantum well has a very small impact on the Landau level splitting for B > 1 T in sharp contrast to the subbands in the absence of a magnetic field. The significance of our findings on the interpretation of Shubnikov-de Haas experiments is discussed.
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| 10. |
- Prevey, J. S., et al.
(författare)
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Warming shortens flowering seasons of tundra plant communities
- 2019
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Ingår i: Nature Ecology & Evolution. - : Springer Science and Business Media LLC. - 2397-334X. ; 3:1, s. 45-52
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Tidskriftsartikel (refereegranskat)abstract
- Advancing phenology is one of the most visible effects of climate change on plant communities, and has been especially pronounced in temperature-limited tundra ecosystems. However, phenological responses have been shown to differ greatly between species, with some species shifting phenology more than others. We analysed a database of 42,689 tundra plant phenological observations to show that warmer temperatures are leading to a contraction of community-level flowering seasons in tundra ecosystems due to a greater advancement in the flowering times of late-flowering species than early-flowering species. Shorter flowering seasons with a changing climate have the potential to alter trophic interactions in tundra ecosystems. Interestingly, these findings differ from those of warmer ecosystems, where early-flowering species have been found to be more sensitive to temperature change, suggesting that community-level phenological responses to warming can vary greatly between biomes.
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