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  • 1
    Electronic Resource
    Electronic Resource
    The electrical hyperfine parameters in synthetic aluminogoethites (1997)
    Springer
    Czechoslovak journal of physics 47 (1997), S. 533-536 
    Details
    ISSN: 1572-9486
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The effects of the aluminum substitution and degree of crystallinity upon the lattice-dynamical and electrical properties of synthetic goethites are determined from their Mössbauer spectra. The temperature variations of the centre shift could be calculated using the Debye approximation for the lattice vibrations. The parameters incorporated in this model exhibit a maximum at a certain aluminum content within each of the four series in this study. It has been found that the principal axis of the EFG remains perpendicular to the direction of the magnetic hyperfine field when the aluminum content and/or the crystallinity change.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1021207406550
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  • 2
    Electronic Resource
    Electronic Resource
    Cellular dissection of the degradation pattern of cortical cell death during aerenchyma formation of rice roots (1998)
    Springer
    Planta 204 (1998), S. 277-287 
    Details
    ISSN: 1432-2048
    Keywords: Key words: Aerenchyma ; Cell death ; Oryza ; Plasmodesma ; Root
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. Cellular events which occur prior to cell collapse were examined in the root cortex of rice (Oryza sativa L.) during aerenchyma formation. Cell collapse started at a specific position in the mid cortex. These cells were distinct in shape from those located towards the periphery. Furthermore, cell collapse was preceded by acidification and the loss of plasma-membrane integrity in cells of the mid cortex. Subsequent death of neighboring cells followed a radial path. Microinjection of molecules of different sizes conjugated with fluorescein isothiocyanate (FITC) showed a molecular exclusion limit of between 9.3 and 19.6 kDa in the root cortex. Furthermore, large molecules, i.e. those around 9.3 kDa, were predominantly transferred in a radial direction, which coincided with the path of sequential cell death.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004250050257
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  • 3
    Electronic Resource
    Electronic Resource
    Cortical cell death, cell proliferation, macromolecular movements and rTip1 expression pattern in roots of rice (Oryza sativa L.) under NaCl stress (1999)
    Springer
    Planta 207 (1999), S. 354-361 
    Details
    ISSN: 1432-2048
    Keywords: Key words: Aerenchyma ; Cell death ; Oryza ; Root ; Stress (NaCl)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. The mode of action of NaCl in terms of cell proliferation and cell death was examined in seminal roots of rice plants (Oryza sativa L.). Salt/sodium chloride was inhibitory to cell number increase and to cell death in cortical tissue, whereas final cortical cell size was the same as in control roots that were not exposed to NaCl. It seems that NaCl may stimulate the transition phase from cell division to cell elongation. Further analysis of the role of NaCl in the suppression of cortical cell death was confined to a delay in the early stage of cell collapse, which was caused by tonoplast disruption, and plasma-membrane destruction. Sodium chloride did not have any effect on the cell-to-cell movement of macromolecules in the root cortex. In-situ hybridization studies indicated that expression of the gene for tonoplast intrinsic protein (rTip1) was localized predominantly in the epidermal and exodermal cells as well as in metaxylem cells in seminal roots. Upon NaCl treatment, the intensity of rTip1 gene expression was raised in the cortical parenchyma, suggesting that salt plays a role in the rapid onset of cell elongation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004250050492
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  • 4
    Electronic Resource
    Electronic Resource
    Regular-like tree expressions (1983)
    Springer
    International journal of parallel programming 12 (1983), S. 1-11 
    Details
    ISSN: 1573-7640
    Keywords: Trees ; regular expressions ; expansive tree grammars ; regularity-preserving transformations ; context-free languages
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Abstract Regular-like expressions provide a compact notation for the explicit description of context-free languages. In this paper we extend these concepts by establishing a one-to-one correspondence between expansive tree languages and regular-like sets of trees. Algorithms are developed for constructing an expansive tree grammar whose language is defined by a given regular-like tree (RLT) expression, and vice versa. These results are then used to obtain RLT equations that describe sets of tree resulting from regularity-preserving transformations associated with three types of errors commonly found in practice.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00996800
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  • 5
    Electronic Resource
    Electronic Resource
    Characterisation of soil-oxide analogs by applied-field 57Fe Mössbauer spectroscopy (1998)
    Springer
    Hyperfine interactions 117 (1998), S. 245-270 
    Details
    ISSN: 1572-9540
    Keywords: Al-substituted iron oxides ; Mössbauer spectroscopy ; external fields
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In this contribution, the effect of high external magnetic fields upon the Mössbauer spectra of aluminous α- and γ-Fe2O3, of aluminous α- and γ-FeOOH and of aluminous Fe3O4 is reviewed. It is shown that the shapes of these spectra are characteristic of these materials and also to some extent of their crystallinities and Al-for-Fe substitutions. Based upon this evaluation, the potential for application of external-field Mössbauer spectroscopy to soil-related analytical purposes is demonstrated for two soil samples. Limitations of the technique are discussed. Finally, some suggestions for further research in this field are indicated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1012643326691
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  • 6
    Electronic Resource
    Electronic Resource
    Mössbauer characterization of iron oxides and (oxy)hydroxides: the present state of the art (2000)
    Springer
    Hyperfine interactions 126 (2000), S. 247-259 
    Details
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Mössbauer spectroscopy is a powerful direct technique for the identification and quantification of iron oxides and (oxy)hydroxides in soils and sediments. However, further characterization with respect to structural properties such as crystallinity, Al substitution, stoichiometry, water content, etc. is rather limited. With some examples of synthetic and natural goethite and hematite sample series it is illustrated that the hyperfine parameters depend on much more structural features than the Al content and crystallinity alone. Neither the Morin transition in hematite nor the Verwey transition in magnetite is directly applicable for analytical purposes in natural samples.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1012603603203
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  • 7
    Electronic Resource
    Electronic Resource
    The effect of Al-content and crystallinity on the magnetic properties of goethites (1999)
    Springer
    Hyperfine interactions 122 (1999), S. 39-46 
    Details
    ISSN: 1572-9540
    Keywords: Al-goethites ; crystallinity ; magnetic properties ; Mössbauer spectroscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract This paper reviews a profound Mössbauer study on the magnetic properties of goethites with varying crystallinity and Al-content. It has been found that both the cluster-ordering and the superferromagnetic models reproduce the temperature dependencies of the average hyperfine fields quite well. However, the magnetic transition temperatures predicted by the cluster-ordering model are in better agreement with those measured from thermoscan experiments. On the other hand, it has been found that the hyperfine field of maximum probability at low temperatures follows the spin–wave law for antiferromagnets. Linear relationships between the saturation hyperfine fields, the inter-sublattice exchange interactions, and the Néel temperatures to the Al-content and crystallinity could be derived. On the other hand, applied-field Mössbauer spectroscopy seems to suggest that the anisotropy field can differentiate between poor crystallinity and Al-content, and that a certain degree of ferrimagnetism occurs at higher Al-contents.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1012681219674
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  • 8
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    Vortex breakdown in compressible flows in pipes (2003)
    American Institute of Physics
    Details
    Publication Date: 2003-08-01
    Print ISSN: 1070-6631
    Electronic ISSN: 1089-7666
    Topics: Physics
    Published by American Institute of Physics
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  • 9
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    Energies, Vol. 12, Pages 3989: Efficient Model Predictive Control with Natural Fault-Tolerance in Asymmetrical Six-Phase Induction Machines (2019)
    MDPI
    In: Energies
    Details
    Publication Date: 2019
    Description: Multiphase machines allow enhancing the performance of wind energy conversion systems from the point of view of reliability and efficiency. The enhanced robustness has been traditionally achieved with a mandatory post-fault control reconfiguration. Nevertheless, when the regulation of x-y currents in multiphase drives is done in open-loop mode, the reconfiguration can be avoided. As a consequence, the reliability of the system increases because fault detection errors or delays have no impact on the post-fault performance. This capability has been recently defined as natural fault tolerance. From the point of view of the efficiency, multiphase machines present a better power density than three-phase machines and lower per-phase currents for the same voltage rating. Moreover, the implementation of control strategies based on a variable flux level can further reduce the system losses. Targeting higher reliability and efficiency for multiphase wind energy conversion systems, this work proposes the implementation of an efficient model predictive control using virtual voltage vectors for six-phase induction machines. The use of virtual voltage vectors allows regulation of the x-y currents in open-loop mode and achieving the desired natural fault tolerance. Then, a higher efficiency can be achieved with a simple and universal cost function, which is valid both in pre- and post-fault situations. Experimental results confirm the viability and goodness of the proposal.
    Electronic ISSN: 1996-1073
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Published by MDPI
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  • 10
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    Energies, Vol. 12, Pages 972: Photovoltaic Power Converter Management in Unbalanced Low Voltage Networks with Ancillary Services Support (2019)
    MDPI
    In: Energies
    Details
    Publication Date: 2019
    Description: The proliferation of residential photovoltaic (PV) prosumers leads to detrimental impacts on the low-voltage (LV) distribution network operation such as reverse power flow, voltage fluctuations and voltage imbalances. This is due to the fact that the strategies for the PV inverters are usually designed to obtain the maximum energy from the panels. The most recent approach to these issues involves new inverter-based solutions. This paper proposes a novel comprehensive control strategy for the power electronic converters associated with PV installations to improve the operational performance of a four-wire LV distribution network. The objectives are to try to balance the currents demanded by consumers and to compensate the reactive power demanded by them at the expense of the remaining converters’ capacity. The strategy is implemented in each consumer installation, constituting a decentralized or distributed control and allowing its practical implementation based on local measurements. The algorithms were tested, in a yearly simulation horizon, on a typical Portuguese LV network to verify the impact of the high integration of the renewable energy sources in the network and the effectiveness and applicability of the proposed approach.
    Electronic ISSN: 1996-1073
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Published by MDPI
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