| 1. |
- Tanja, S, et al.
(författare)
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Air temperature triggers the recovery of evergreen boreal forest photosynthesis in spring
- 2003
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Ingår i: Global Change Biology. - : Wiley. - 1354-1013. ; 9:10, s. 1410-1426
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Tidskriftsartikel (refereegranskat)abstract
- The timing of the commencement of photosynthesis (P-*) in spring is an important determinant of growing-season length and thus of the productivity of boreal forests. Although controlled experiments have shed light on environmental mechanisms triggering release from photoinhibition after winter, quantitative research for trees growing naturally in the field is scarce. In this study, we investigated the environmental cues initiating the spring recovery of boreal coniferous forest ecosystems under field conditions. We used meteorological data and above-canopy eddy covariance measurements of the net ecosystem CO2 exchange (NEE) from five field stations located in northern and southern Finland, northern and southern Sweden, and central Siberia. The within- and intersite variability for P-* was large, 30-60 days. Of the different climate variables examined, air temperature emerged as the best predictor for P-* in spring. We also found that 'soil thaw', defined as the time when near-surface soil temperature rapidly increases above 0degreesC, is not a useful criterion for P-*. In one case, photosynthesis commenced 1.5 months before soil temperatures increased significantly above 0degreesC. At most sites, we were able to determine a threshold for air-temperature-related variables, the exceeding of which was required for P-*. A 5-day running-average temperature (T-5) produced the best predictions, but a developmental-stage model (S) utilizing a modified temperature sum concept also worked well. But for both T-5 and S, the threshold values varied from site to site, perhaps reflecting genetic differences among the stands or climate-induced differences in the physiological state of trees in late winter/early spring. Only at the warmest site, in southern Sweden, could we obtain no threshold values for T-5 or S that could predict P-* reliably. This suggests that although air temperature appears to be a good predictor for P-* at high latitudes, there may be no unifying ecophysiological relationship applicable across the entire boreal zone.
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| 2. |
- Shi, X., et al.
(författare)
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Quantitative assessment of structural and compositional colors induced by femtosecond laser : A case study on 301LN stainless steel surface
- 2019
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Ingår i: Applied Surface Science. - : Elsevier B.V.. - 0169-4332 .- 1873-5584. ; 484, s. 655-662
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Tidskriftsartikel (refereegranskat)abstract
- The topic of durable coloration and passivation of metal surfaces using state-of-the-art techniques has gained enormous attention and devotion with unremitting efforts of researchers worldwide. Although femtosecond laser marking has been performed on many metals, the related coloration mechanisms are mainly referred to structural colors produced by the interaction of visible light with periodic surface structures. Yet, general quantitative determination of the resulting colors and their origins remain elusive. In this work, we realized quantitative separations of structural colors and compositional pigmentary colors on 301LN austenitic stainless steel surfaces that were treated by femtosecond laser machining. The overall color information was extracted from surface reflectance, with structural color given by numerical simulations, and oxide compositions by chemical state analysis. It was shown that the laser-induced apparent colors of 301LN steel surfaces were combinations of structural and compositional colorations, with the former dominating the angular response and the latter setting up the brownish bases. In addition to the quantification of colors, the analysis method in this work may be useful for the generation and specification of tailored color palettes for practical coloration on metal surfaces by femtosecond laser marking.
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| 3. |
- Andersson, T., et al.
(författare)
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Electronic structure transformation in small bare Au clusters as seen by x-ray photoelectron spectroscopy
- 2017
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Ingår i: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 50:1
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Tidskriftsartikel (refereegranskat)abstract
- Free bare gold clusters in the size range from few tens to few hundred atoms (<= 1 nm dimensions) have been produced in a beam, and the size-dependent development of their full valence band including the 5d and 6s parts has been mapped 'on the fly' by synchrotron-based photoelectron spectroscopy. The Au 4f core level has been also probed, and the cluster-specific Au 4f ionization energies have been used to estimate the cluster size. The recorded in the present work valence spectra of the small clusters are compared with the spectra of the large clusters (N similar to 10(3)) created by us using a magnetron-based gas aggregation source. The comparison shows a substantially narrower 5d valence band and the decrease in its splitting for gold clusters in the size range of few hundred atoms and below. Our DFT calculations involving the pseudopotential method show that the 5d band width of the ground state increases with the cluster size and by the size N = 20 becomes comparable with the experimental width of the valence photoelectron spectrum. Similar to the earlier observations on supported clusters we interpret our experimental and theoretical results as due to the undercoordination of a large fraction of atoms in the clusters with N similar to 10(2) and below. The consequences of such electronic structure of small gold clusters are discussed in connection with their specific physical and chemical properties related to nanoplasmonics and nanocatalysis.
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| 4. |
- Boudjemia, N., et al.
(författare)
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Deep-core photoionization of krypton atoms below and above the 1s ionization threshold
- 2020
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Ingår i: Physical Review A: covering atomic, molecular, and optical physics and quantum information. - : AMER PHYSICAL SOC. - 2469-9926 .- 2469-9934. ; 101:5
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Tidskriftsartikel (refereegranskat)abstract
- Electronic relaxation of atomic Kr below and above the 1s ionization threshold is investigated experimentally using hard x-ray photoelectron spectroscopy. The experimental results are interpreted with the aid of relativistic Dirac-Fock calculations. The 1s orbital core-hole lifetime is extracted and the satellite's structures accompanying the photoelectron main line are assigned. Auger spectra recorded below and above the K edge are also investigated. In particular, the Auger cascade originating from vacancies of different origin in the L shell is analyzed in great detail. Competition between radiative KL versus nonradiative KLL Auger emission is emphasized.
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| 5. |
- Boudjemia, N., et al.
(författare)
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Electron spectroscopy and dynamics of HBr around the Br 1s(-1) threshold
- 2020
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 22:46, s. 26806-26818
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Tidskriftsartikel (refereegranskat)abstract
- A comprehensive electron spectroscopic study combined with partial electron yield measurements around the Br 1s ionization threshold of HBr at approximately equal to 13.482 keV is reported. In detail, the Br 1s(-1) X-ray absorption spectrum, the 1s(-1) photoelectron spectrum as well as the normal and resonant KLL Auger spectra are presented. Moreover, the L-shell Auger spectra measured with photon energies below and above the Br 1s(-1) ionization energy as well as on top of the Br 1s(-1)sigma* resonance are shown. The latter two Auger spectra represent the second step of the decay cascade subsequent to producing a Br 1s(-1) core hole. The measurements provide information on the electron and nuclear dynamics of deep core-excited states of HBr on the femtosecond timescale. From the different spectra the lifetime broadening of the Br 1s(-1) single core-hole state as well as of the Br(2s(-2),2s(-1)2p(-1),2p(-2)) double core-hole states are extracted and discussed. The slope of the strongly dissociative HBr 2p(-2)sigma* potential energy curve is found to be about -13.60 eV angstrom(-1). The interpretation of the experimental data, and in particular the assignment of the spectral features in the KLL and L-shell Auger spectra, is supported by relativistic calculations for HBr molecule and atomic Br.
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| 6. |
- Boudjemia, N., et al.
(författare)
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Experimental and theoretical study of the Kr L-shell Auger decay
- 2021
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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. ; 104:1
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Tidskriftsartikel (refereegranskat)abstract
- The LMM Auger spectra of krypton are measured using the photon energies hv = 1709 eV, 1792 eV, 1950 eV, and 13 keV. This approach allows separating the contributions from the various core holes L-1 , L-2., and L-3. Previously unobserved transitions are presented. Complementary theoretical work is performed allowing the assignment of the spectral features. The L2,3Y -MMY (Y = M-4,M-5, N-1,N-2,N-3) Auger transitions of Kr2+ formed via Coster-Kronig Auger decay of the core holes L-1 and L-2. are also investigated. These spectra comprise about 4000 and 13 000 transitions, respectively, so that only general statements on the assignment, such as the configurations involved in the transitions, can be given.
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| 7. |
- Ceolin, D., et al.
(författare)
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Auger resonant-Raman study at the Ar K edge as probe of electronic-state-lifetime interferences
- 2015
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 91:2
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Tidskriftsartikel (refereegranskat)abstract
- The resonant-Auger decay in argon following Ar 1s - np excitations was studied under resonant-Raman conditions, i.e., with a total instrumental bandwidth much narrower than the natural linewidth of the absorption features. These state-of-the-art experiments are combined with a radiationless resonant-Raman scattering theory. The main results include identification of the energy position of some high-lying Rydberg states previously masked by insufficient resolution and clear evidence of electronic-state-lifetime interference phenomena.
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| 8. |
- Hautala, Lauri, et al.
(författare)
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Experimental observation of structural phase transition in CsBr clusters
- 2017
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Ingår i: Physical Review B. - 1098-0121. ; 95:4
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Tidskriftsartikel (refereegranskat)abstract
- Formation and growth of CsBr clusters embedded in unsupported Ar clusters was studied using synchrotron radiation photoelectron spectroscopy. The development of the core-level electronic structure for cluster sizes between a few and a few hundred atoms contained information about the local coordination of the constituent particles. The experimental results indicate that a gradual structural phase transition from NaCl structure to CsCl structure for CsBr clusters takes place at around 160 atoms per cluster.
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| 9. |
- Mikkela, M. -H., et al.
(författare)
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Size-dependent study of Rb and K clusters using core and valence level photoelectron spectroscopy
- 2011
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Ingår i: European Physical Journal D. Atomic, Molecular, Optical and Plasma Physics. - : Springer Science and Business Media LLC. - 1434-6060 .- 1434-6079. ; 64:2-3, s. 347-352
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Tidskriftsartikel (refereegranskat)abstract
- Electronic structure of free and neutral Rb and K clusters containing from few tens to few hundred atoms has been studied using synchrotron radiation. Core-level photoelectron spectroscopy has been used to probe the metallic nature of Rb and K clusters. We show that the metallicity exists down to the dimensions of few nanometers. Simultaneously the emergence and evolution of the valence band structure has been monitored by the valence-level photoelectron spectroscopy.
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| 10. |
- Piancastelli, Maria Novella, et al.
(författare)
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X-ray versus Auger emission following Xe 1s photoionization
- 2017
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 95:6
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Tidskriftsartikel (refereegranskat)abstract
- Xe 1s photoelectron spectra were measured at SPring-8, Japan. The core-hole lifetime broadening was found to be 9.6 eV, yielding a lifetime of similar to 68 as. The amount of radiative versus nonradiative decay was assessed by recording Auger LMM spectra below and above the K edge. Below the K edge, L vacancies are produced only by direct photoionization, while above the K edge some of these vacancies are mainly produced by KL emission following 1s photoionization. Due to the dipole selection rule for x-ray emission, the dominant role of the KL relaxation process is rather directly observed.
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| 11. |
- Pilla, Rachel M., et al.
(författare)
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Deeper waters are changing less consistently than surface waters in a global analysis of 102 lakes
- 2020
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 10:1
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Tidskriftsartikel (refereegranskat)abstract
- Globally, lake surface water temperatures have warmed rapidly relative to air temperatures, but changes in deepwater temperatures and vertical thermal structure are still largely unknown. We have compiled the most comprehensive data set to date of long-term (1970–2009) summertime vertical temperature profiles in lakes across the world to examine trends and drivers of whole-lake vertical thermal structure. We found significant increases in surface water temperatures across lakes at an average rate of + 0.37 °C decade−1, comparable to changes reported previously for other lakes, and similarly consistent trends of increasing water column stability (+ 0.08 kg m−3 decade−1). In contrast, however, deepwater temperature trends showed little change on average (+ 0.06 °C decade−1), but had high variability across lakes, with trends in individual lakes ranging from − 0.68 °C decade−1 to + 0.65 °C decade−1. The variability in deepwater temperature trends was not explained by trends in either surface water temperatures or thermal stability within lakes, and only 8.4% was explained by lake thermal region or local lake characteristics in a random forest analysis. These findings suggest that external drivers beyond our tested lake characteristics are important in explaining long-term trends in thermal structure, such as local to regional climate patterns or additional external anthropogenic influences.
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| 12. |
- Pilla, Rachel M., et al.
(författare)
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Global data set of long-term summertime vertical temperature profiles in 153 lakes
- 2021
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Ingår i: Scientific Data. - : Springer Nature. - 2052-4463. ; 8:1
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Tidskriftsartikel (refereegranskat)abstract
- Climate change and other anthropogenic stressors have led to long-term changes in the thermal structure, including surface temperatures, deepwater temperatures, and vertical thermal gradients, in many lakes around the world. Though many studies highlight warming of surface water temperatures in lakes worldwide, less is known about long-term trends in full vertical thermal structure and deepwater temperatures, which have been changing less consistently in both direction and magnitude. Here, we present a globally-expansive data set of summertime in-situ vertical temperature profiles from 153 lakes, with one time series beginning as early as 1894. We also compiled lake geographic, morphometric, and water quality variables that can influence vertical thermal structure through a variety of potential mechanisms in these lakes. These long-term time series of vertical temperature profiles and corresponding lake characteristics serve as valuable data to help understand changes and drivers of lake thermal structure in a time of rapid global and ecological change.
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| 13. |
- Tchaplyguine, Maxim, et al.
(författare)
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Size-dependent evolution of electronic structure in neutral Pb clusters-As seen by synchrotron-based X-ray photoelectron spectroscopy
- 2014
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Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048 .- 1873-2526. ; 195, s. 55-61
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Tidskriftsartikel (refereegranskat)abstract
- Neutral Pb clusters in the size range from a few tens of atoms up to similar to 100 atoms are studied using synchrotron-based photoelectron spectroscopy. The electronic structure is seen to differ increasingly from that of the solid when the cluster size decreases. The valence band narrows gradually - down to about one fifth of the solid-state band width at the smallest size of few tens of atoms. Simultaneously the Fermi-edge energy shifts further away from the solid value by more than 2 eV. The Pb 5d core level binding energy also increases and the spectral features broaden and change in shape. The changes observed for the valence and for the 5d response energies and shapes are discussed in the context of the metal-to-insulator transition observed earlier in Pb clusters below the critical size of 20-30 atoms/cluster. (C) 2014 Elsevier B.V. All rights reserved.
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| 14. |
- Urpelainen, S., et al.
(författare)
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FINEST:A high performance branch-line for VUV photon energy range gas phase studies at MAX-lab
- 2010
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Ingår i: AIP Conference Proceedings. - : AIP. - 0094-243X. - 9780735407824 ; 1234, s. 411-414
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Konferensbidrag (refereegranskat)abstract
- We present a dedicated beamline branch for high flux and ultra-high resolution (R>100000) gas and vapor phase studies in the vacuum-ultra-violet (VUV) region of light on the undulator beamline I3, located on the 700 MeV MAX-III storage ring. The mechanical and optical design of the branch-line, the differential pumping setup as well as performance characteristics are presented.
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| 15. |
- Wang, W., et al.
(författare)
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A new user-friendly materials science end station at the FinEstBeAMS beamline of MAX IV
- 2022
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Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 2380
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Konferensbidrag (refereegranskat)abstract
- FinEstBeAMS is an atmospheric and materials science beamline located at the 1.5 GeV storage ring of the MAX IV Laboratory in Lund, Sweden. It offers a very wide photon energy range 4.5-1300 eV and radiation with different polarization characteristics. The beamline has three end stations installed at two branch lines. The new solid state end station (SSES) is described in this paper. It is a high-throughput apparatus with flexible sample preparation options for X-ray photoemission, angle-resolved photoemission, and X-ray absorption spectroscopy. Three examples of experiments at room temperature demonstrate the capabilities of the SSES in the research field of surface science and condensed matter physics.
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