| 1. |
- Szlachetko, Jakub, et al.
(författare)
-
Establishing nonlinearity thresholds with ultraintense X-ray pulses
- 2016
-
Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 6
-
Tidskriftsartikel (refereegranskat)abstract
- X-ray techniques have evolved over decades to become highly refined tools for a broad range of investigations. Importantly, these approaches rely on X-ray measurements that depend linearly on the number of incident X-ray photons. The advent of X-ray free electron lasers (XFELs) is opening the ability to reach extremely high photon numbers within ultrashort X-ray pulse durations and is leading to a paradigm shift in our ability to explore nonlinear X-ray signals. However, the enormous increase in X-ray peak power is a double-edged sword with new and exciting methods being developed but at the same time well-established techniques proving unreliable. Consequently, accurate knowledge about the threshold for nonlinear X-ray signals is essential. Herein we report an X-ray spectroscopic study that reveals important details on the thresholds for nonlinear X-ray interactions. By varying both the incident X-ray intensity and photon energy, we establish the regimes at which the simplest nonlinear process, two-photon X-ray absorption (TPA), can be observed. From these measurements we can extract the probability of this process as a function of photon energy and confirm both the nature and sub-femtosecond lifetime of the virtual intermediate electronic state.
|
|
| 2. |
- Baunsgaard, C. B., et al.
(författare)
-
EXOSKELETON GAIT TRAINING AFTER SPINAL CORD INJURY: AN EXPLORATORY STUDY ON SECONDARY HEALTH CONDITIONS
- 2018
-
Ingår i: Journal of Rehabilitation Medicine. - : Medical Journals Sweden AB. - 1650-1977 .- 1651-2081. ; 50:9, s. 806-813
-
Tidskriftsartikel (refereegranskat)abstract
- Objective: To explore changes in pain, spasticity, range of motion, activities of daily living, bowel and lower urinary tract function and quality of life of individuals with spinal cord injury following robotic exoskeleton gait training. Methods: Three training sessions per week for 8 weeks using an Ekso GT robotic exoskeleton (Ekso Bionics). Included were individuals with recent (<1 year) or chronic (>1 year) injury, paraplegia and tetraplegia, complete and incomplete injury, men and women. Results: Fifty-two participants completed the training protocol. Pain was reported by 52% of participants during the week prior to training and 17% during training, but no change occurred longitudinally. Spasticity decreased after a training session compared with before the training session (p< 0.001), but not longitudinally. Chronically injured participants increased Spinal Cord Independence Measure (SCIM III) from 73 to 74 (p= 0.008) and improved life satisfaction (p= 0.036) over 8 weeks of training. Recently injured participants increased SCIM III from 62 to 70 (p<0.001), but no significant change occurred in life satisfaction. Range of motion, bowel and lower urinary function did not change over time. Conclusion: Training seemed not to provoke new pain. Spasticity decreased after a single training session. SCIM III and quality of life increased longitudinally for subsets of participants.
|
|
| 3. |
- König, C.F.J., et al.
(författare)
-
Mechanistic studies of chemical looping desulfurization of Mn-based oxides using in situ X-ray absorption spectroscopy
- 2014
-
Ingår i: Applied Energy. - : Elsevier BV. - 1872-9118 .- 0306-2619. ; 113, s. 1895-1901
-
Tidskriftsartikel (refereegranskat)abstract
- Cleaning of producer gas from biomass gasification is required for further processing, e.g. to avoid catalyst poisoning in subsequent conversion steps. High-temperature gas cleaning, of which sulfur removal is an important part, is a promising way to improve the overall efficiency of biomass conversion. In a high temperature "chemical looping desulfurization" process, a sorbent material, here manganese oxide, is cycled between producer gas from the gasifier to remove sulfur species, and an oxidizing atmosphere, in which the sulfur species are released as SO2. Alternatively, the use of such material as reactive bed material could be integrated into an allothermal dual fluidized bed gasifier. In a laboratory reactor, we subjected manganese-based materials to a periodically changing gas atmosphere, simulating a "chemical looping desulfurization" reactor. The "fuel reactor" gas contained H2, CO, CH4 and H2S, similar as in the producer gas, and the "oxidizing reactor" contained diluted O2. Mass spectrometry showed that most of the H2S is taken up by the sample in the "fuel reactor" part, while also some unwanted SO2 is generated in the "fuel reactor" part. Most of the sulfur is released in the oxidizing reactor. Simultaneous in situ X-ray absorption spectroscopy (XAS) of the Mn materials during different stages of the chemical looping desulfurization process showed that the initial Mn3O4 is transformed in the presence of H2S to MnS via a MnO intermediate in the fuel reactor. Oxygen from the reduction of Mn3O4 oxidizes some H2S to the undesired SO2 in the fuel reactor. Upon exposure to O2, MnS is again oxidized to Mn3O4 via MnO, releasing SO2. The presence of CO and/or CH4 in the fuel reactor has no effect on this mechanism. Measuring the structure-performance relationship of gas cleaning materials with in situ methods will enable knowledge-based materials development for improved performance. © 2013 Elsevier Ltd. All rights reserved.
|
|
| 4. |
|
|
| 5. |
- Friberg, Ida, 1990, et al.
(författare)
-
Structure and performance of zeolite supported Pd for complete methane oxidation
- 2021
-
Ingår i: Catalysis Today. - : Elsevier BV. - 0920-5861. ; 382, s. 3-12
-
Tidskriftsartikel (refereegranskat)abstract
- The influence of zeolite support materials and their impact on CH oxidation activity was studied utilizing Pd supported on H-beta and H-SSZ-13. A correlation between CH oxidation activity, Si/Al ratio (SAR), the type of zeolite framework, reduction-oxidation behaviour, and Pd species present was found by combining catalytic activity measurements with a variety of characterization methods (operando XAS, NH -TPD, SAXS, STEM and NaCl titration). Operando XAS analysis indicated that catalysts with high CH oxidation activity experienced rapid transitions between metallic- and oxidized-Pd states when switching between rich and lean conditions. This behaviour was exhibited by catalysts with dispersed Pd particles. By contrast, the formation of ion-exchanged Pd and large Pd particles appeared to have a detrimental effect on the oxidation-reduction behaviour and the conversion of CH . The formation of ion-exchanged Pd and large Pd particles was limited by using a highly siliceous beta zeolite support with a low capacity for cation exchange. The same effect was also found using a small-pore SSZ-13 zeolite due to the lower mobility of Pd species. It was found that the zeolite support material should be carefully selected so that the well-dispersed Pd particles remain, and the formation of ion-exchanged Pd is minimized. 4 4 3 4 4 2+ 2+ 2+
|
|
| 6. |
- Szlachetko, Jakub, et al.
(författare)
-
Subsecond and in situ chemical speciation of Pt/Al(2)O(3) during oxidation-reduction cycles monitored by high-energy resolution off-resonant X-ray spectroscopy.
- 2013
-
Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 135:51, s. 19071-4
-
Tidskriftsartikel (refereegranskat)abstract
- We report an in situ time-resolved high-energy resolution off-resonant spectroscopy study with subsecond resolution providing insight into the oxidation and reduction steps of a Pt catalyst during CO oxidation. The study shows that the slow oxidation step is composed of two characteristic stages, namely, dissociative adsorption of oxygen followed by partial oxidation of Pt subsurface. By comparing the experimental spectra with theoretical calculations, we found that the intermediate chemisorbed O on Pt is adsorbed on atop position, which suggests surface poisoning by CO or surface reconstruction.
|
|
