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| 2. |
- Palmqvist, A. E. C., et al.
(författare)
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A crystalline microporous narrow-bandgap semiconductor
- 2004
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Ingår i: Angewandte Chemie International Edition. - : Wiley. - 1433-7851 .- 1521-3773. ; 43:6, s. 700-704
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Tidskriftsartikel (refereegranskat)abstract
- A crystalline microporous semiconductor |(| K6(H 2O)6| [Sb12O18])3| [Te36] (denoted SBC-1) has been prepared, which consists of 24-ring tubular tellurium units that host 12-ring {Sb12O18} tubular units, which in turn act as hosts for K+ ions and H 2O molecules (see picture). An example of a second-order zeoate, it has a narrow bandgap of 0.25 eV and exhibits highly anisotropic electrical conductivity.
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| 3. |
- Bjurhager, Ingela, et al.
(författare)
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State of degradation in archeological oak from the 17th century vasa ship : Substantial strength loss correlates with reduction in (holo)cellulose molecular weight
- 2012
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Ingår i: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; :8, s. 2521-2527
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Tidskriftsartikel (refereegranskat)abstract
- In 1628, the Swedish warship Vasa capsized on her maiden voyage and sank in the Stockholm harbor. The ship was recovered in 1961 and, after polyethylene glycol (PEG) impregnation, it was displayed in the Vasa museum. Chemical investigations of the Vasa were undertaken in 2000, and extensive holocellulose degradation was reported at numerous locations in the hull. We have now studied the longitudinal tensile strength of Vasa oak as a function of distance from the surface. The PEG-content, wood density, and cellulose microfibril angle were determined. The molar mass distribution of holocellulose was determined as well as the acid and iron content. A good correlation was found between the tensile strength of the Vasa oak and the average molecular weight of the holocellulose, where the load-bearing cellulose microfibril is the critical constituent. The mean tensile strength is reduced by approximately 40%, and the most affected areas show a reduction of up to 80%. A methodology is developed where variations in density, cellulose microfibril angle, and PEG content are taken into account, so that cell wall effects can be evaluated in wood samples with different rate of impregnation and morphologies.
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| 4. |
- Christensen, M, et al.
(författare)
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Structural study of Fe doped and Ni substituted thermoelectric skutterudites by combined synchrotron and neutron powder diffraction and ab initio theory
- 2004
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 96:6, s. 3148-3157
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Tidskriftsartikel (refereegranskat)abstract
- We present neutron and synchrotron powder-diffraction investigations as well as ab initio calculations to elucidate delicate structural features in doped skutterudites. Samples with assumed Fe doping were investigated (FeyCo4Sb12, y=0.4, 0.8, 1.0, and 1.6), as well as samples with formal Ni substitution (Co4-xNixSb12, x=0, 0.4, 0.8, and 1.2). The present study serves as a case story for the determination of fine structural details of thermoelectric skutterudites by diffraction methods in combination with ab initio calculations. We illustrate the problem of fluorescence in the conventional x-ray powder diffraction on the Fe-doped samples by a comparison with the neutron powder-diffraction data. On the series of the Ni-substituted samples, the neutron powder-diffraction data were collected to investigate the exact sitting of the Ni. The sample with the highest Ni substitution (Co2.8Ni1.2Sb12) was also used for high resolution, high-energy synchrotron powder diffraction measurements. These revealed that the sample consists of two skutterudite phases. A complete description of the Ni-substituted samples was obtained in tandem with ab initio calculations, which show that the system contains a Ni-rich (Co0.38Ni3.62Sb12) and a Ni-poor (Co3.76Ni0.24Sb12)) skutterudite phases.
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| 5. |
- Iversen, Michael, et al.
(författare)
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Tower of two-dimensional scar states in a localized system
- 2024
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Ingår i: Physical Review A: covering atomic, molecular, and optical physics and quantum information. - : American Physical Society (APS). - 2469-9926 .- 2469-9934. ; 109:2
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Tidskriftsartikel (refereegranskat)abstract
- The eigenstate thermalization hypothesis describes how most isolated many-body quantum systems reach thermal equilibrium. However, the hypothesis is violated by phenomena such as many-body localization and quantum many-body scars. In this work, we study a finite, two-dimensional, disordered model hosting a tower of scar states. This construction is a particular instance of a general framework and we demonstrate its generality by constructing two disordered models hosting a different tower of scar states. At weak disorder, we find numerically that the spectra are nonthermal, and the scar states appear as exact eigenstates with high entropy for certain bipartitions. At strong disorder, the spectra localize and the scar states are identified as inverted scars since the scar states are embedded in a localized background as opposed to a thermal background. We argue that, for the considered type of models, the localization is stronger than what would be naively expected, and we show this explicitly for one of the models. The argument also provides guidelines for obtaining similarly strong localization in other scarred models. We study the transition from the thermal phase to localization by observing the adjacent gap ratio shifting from the Wigner surmise to the Poisson distribution with increasing disorder strength. Moreover, the entanglement entropy transitions from volume-law scaling with system size at weak disorder to area-law scaling at strong disorder. Finally, we demonstrate that localization protects scar revivals for initial states with partial support in the scar subspace.
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| 6. |
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| 7. |
- Nilsson, Helena, et al.
(författare)
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A non-solvent approach for high-stiffness all-cellulose biocomposites based on pure wood cellulose
- 2010
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Ingår i: Composites Science And Technology. - : Elsevier BV. - 0266-3538 .- 1879-1050. ; 70:12, s. 1704-1712
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Tidskriftsartikel (refereegranskat)abstract
- All-cellulose composites are commonly prepared using cellulose solvents. In this study, moldable all-cellulose I wood fiber materials of high cellulose purity (97%) were successfully compression molded. Water is the only processing aid. The material is interesting as a "green" biocomposite for industrial applications. Dissolving wood fiber pulps (Eucalyptus hardwood and conifer softwood) are used and the influence of pulp origin, beating and pressing temperature (20-180 degrees C) on supramolecular cellulose nanostructure is studied by solid state CP/MAS C-13 NMR. Average molar mass is determined by SEC to assess process degradation effects. Mechanical properties are determined in tensile tests. High-density composites were obtained with a Young's modulus of up to 13 GPa. In addition, nanoscale cellulose fibril aggregation was confirmed due to processing, and resulted in a less moisture sensitive material.
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| 8. |
- Nilsson, Helena, et al.
(författare)
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Compression molded wood pulp biocomposites : A study of hemicellulose influence on cellulose supramolecular structure and material properties
- 2012
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Ingår i: Cellulose. - : Springer Science and Business Media LLC. - 0969-0239 .- 1572-882X. ; 19:3, s. 751-760
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Tidskriftsartikel (refereegranskat)abstract
- In this study, the importance of hemicellulose content and structure in chemical pulps on the property relationships in compression molded wood pulp biocomposites is examined. Three different softwood pulps are compared; an acid sulfite dissolving grade pulp with high cellulose purity, an acid sulfite paper grade pulp and a paper grade kraft pulp, the latter two both containing higher amounts of hemicelluloses. Biocomposites based the acid sulfite pulps exhibit twice as high Young's modulus as the composite based on paper grade kraft pulp, 11-12 and 6 GPa, respectively, and the explanation is most likely the difference in beating response of the pulps. Also the water retention value (WRV) is similarly low for the two molded sulfite pulps (0.5 g/g) as compared to the molded kraft pulp (0.9 g/g). The carbohydrate composition is determined by neutral sugar analysis and average molar masses by SEC. The cellulose supramolecular structure (cellulose fibril aggregation) is studied by solid state CP/MAS 13C-NMR and two forms of hemicellulose are assigned. During compression molding, cellulose fibril aggregation occurs to higher extent in the acid sulfite pulps as compared to the kraft pulp. In conclusion, the most important observation from this study is that the difference in hemicellulose content and structure seems to affect the aggregation behaviour and WRV of the investigated biocomposites.
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| 9. |
- Stiewe, C, et al.
(författare)
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Nanostructured Co1-xNix(Sb1-yTey)(3) skutterudites : Theoretical modeling, synthesis and thermoelectric properties
- 2005
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 97:4
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Tidskriftsartikel (refereegranskat)abstract
- The properties of Te-doped Co(Sb1-yTey)(3) and Te-Ni double-doped Co1-xNix(Sb1-yTey)(3) nanostructured skutterudites were evaluated by means of x-ray powder diffraction, and transport properties measured on the synthesized samples have been compared with ab initio theoretical modeling. Theoretical optimal dopant contents have been evaluated according to the maximum value of the power factor, calculating the electronic transport properties from the ab initio material band structure using semiclassical Boltzmann transport theory. The samples have been synthesized by chemical alloying with Te substitution for Sb up to 2.5 at. % and Ni substitution for Co up to 2.0 at. %. X-ray powder diffraction has been performed on all samples to reveal information about phase purity and Rietveld refinement was performed for the phase composition and cell parameter. The thermoelectric properties of the resulting consolidates were investigated in a temperature range from 300 to 723 K using various measurement facilities. A standardization and round robin program was started among the participating evaluation laboratories in order to ensure reliability of the data obtained. The significant reduction in thermal conductivity, when compared to highly annealed CoSb3, could be proved which is caused by the nanostructuring, resulting in a high concentration of grain boundaries. A combination of substitution levels for Ni and Te has been found resulting in the largest ZT value of 0.65 at 680 K among unfilled skutterudite materials.
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| 10. |
- Wickholm, K., et al.
(författare)
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Quantification of cellulose forms in complex cellulose materials : A chemometric model
- 2001
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Ingår i: Cellulose. - Stockholm : Kluwer Academic Publishers. - 0969-0239 .- 1572-882X. ; 8:2, s. 139-148
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we present a chemometric model for quantifying the cellulose forms with different states of order found within cellulose I fibrils. The relative amounts of the different cellulose forms, that is crystalline cellulose I, para-crystalline cellulose and cellulose at accessible and inaccessible cellulose surfaces, were determined by non-linear least squares fitting of the C4-region in CP/MAS C-13-NMR (Cross-Polarisation Magic Angle Spinning Carbon-13 Nuclear Magnetic Resonance) spectra. By correlating these results from the C4-region with the full spectral data we obtained a model which is able to provide an assessment of the relative amounts of the different cellulose forms directly from NMR-spectra of complex lignocellulosic samples. Furthermore, this model enabled new assignments to be made in the C1-region for signals from cellulose at accessible fibril surfaces.
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