| 1. |
- Canales, Javier, et al.
(författare)
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Gene expression profiling in the stem of young maritime pine trees : detection of ammonium stress-responsive genes in the apex
- 2011
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Ingår i: Trees. - : Springer Science and Business Media LLC. - 0931-1890 .- 1432-2285. ; 26:2, s. 609-619
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Tidskriftsartikel (refereegranskat)abstract
- The shoots of young conifer trees represent an interesting model to study the development and growth of conifers from meristematic cells in the shoot apex to differentiated tissues at the shoot base. In this work, microarray analysis was used to monitor contrasting patterns of gene expression between the apex and the base ofmaritime pine shoots. A group of differentially expressed genes were selected and validated by examining their relative expression levels in different sections along thestem, from the top to the bottom. After validation of the microarray data, additional geneexpression analyses were also performed in the shoots of young maritime pine treesexposed to different levels of ammonium nutrition. Our results show that the apex ofmaritime pine trees is extremely sensitive to conditions of ammonium excess or deficiency, as revealed by the observed changes in the expression of stress-responsivegenes. This new knowledge may be used to precocious detection of early symptoms of nitrogen nutritional stresses, thereby increasing survival and growth rates of young treesin managed forests.
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| 2. |
- Ariza, David, et al.
(författare)
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Electrical Conduction Currents Prior to Negative Streamer Inception in Mineral-Oil/Solid Interfaces
- 2021
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Ingår i: IEEE transactions on dielectrics and electrical insulation. - : Institute of Electrical and Electronics Engineers (IEEE). - 1070-9878 .- 1558-4135. ; 28, s. 1300-1307
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Tidskriftsartikel (refereegranskat)abstract
- This paper is an experimental study of the electrical conduction of mineral-oil/solid interfaces in negative polarity. This study is performed in a point-plane configuration immersed in mineral oil submitted to impulse voltages. The interface is assembled with an inclined solid in contact with the point electrode tip. Charge recordings and conduction currents of different combinations of mineral-oil/solid interfaces are reported. Different polymers and oil-impregnated papers are used as the solid materials. It is found that for voltages lower than the inception voltage, the injection of charge belongs to a weak injection regime. The spatial limitation with solids of similar permittivity as the mineral oil decreases the charge injection. The charge injection at mineral-oil/solid interfaces follow two conduction current type characteristics. Experiments with mineral-oil/PTFE interface shows the existence of a transition between both conduction current types if the applied voltage is increased.
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| 3. |
- Ariza, David, et al.
(författare)
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First Mode Negative Streamers along Mineral Oil-solid Interfaces
- 2017
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Ingår i: IEEE transactions on dielectrics and electrical insulation. - : IEEE. - 1070-9878 .- 1558-4135. ; 24:4
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Tidskriftsartikel (refereegranskat)abstract
- This document presents an experimental study on the propagation of first mode negative streamers along mineral oil-solid interfaces. Samples made of an oil impregnated kraft paper and a low-porosity paper made from cellulosic micro and nano fibrils, as well as different polymeric films (low density polyethylene (LDPE), polyethylene terephthalate (PET), polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF)) are used as the solid. A comparison of the length, charge and velocity of streamers for all different mineral oil-solid interfaces is reported. It is shown that streamers propagate longer and faster along mineral oil-solid interfaces with low surface roughness, low porosity and higher electrical permittivity than mineral oil. Those streamers show a quasi-continuous injection of charge in the early stage of their propagation. This quasi-continuous charge injection consists of a sequence of small charge steps separated by few tens of nanoseconds in between. In comparison, the streamers that propagate along surfaces with similar permittivity to the mineral oil have lower injection of charge and higher stopping voltage conditions than streamers propagating free in the liquid without any solid barrier.
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| 4. |
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| 5. |
- Ariza, David, et al.
(författare)
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First-Mode of Negative Streamers: Inception at Liquid/Solid Interfaces
- 2021
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Ingår i: High Voltage. - : Institution of Engineering and Technology (IET). - 2397-7264.
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Tidskriftsartikel (refereegranskat)abstract
- An experimental study of the inception of the first-mode negative streamer at liquid/solid interfaces is presented in this article. The study is performed with a point-plane configuration under square high voltage pulses. The electrode configuration is immersed in mineral oil and the liquid/solid interface is assembled in contact with the point electrode or in its vicinity. Four polymers and two impregnated papers have been tested as solids of the liquid/solid interface. Thus, it is possible to compare the influence of different parameter of the solid and the interface on the streamer inception. For example: Permittivity, solid surface roughness, chemical composition, etc. It has been observed that streamer inception voltages at interfaces with solids of higher permittivity to that of the mineral oil are statistically similar. Additionally, streamer inception voltages of streamer initiated free in the oil (no liquid/solid interface) are similar to that of the inception voltage of cases with solids with high permittivity. In contrast, the inception voltage of streamers initiated at permittivity matched interfaces are shown to be highest of the cases. The streamer inception voltage is also studied for different distances between the liquid/solid interface and the point electrode with a permittivity matched interface. The results show a dependency of the inception voltage and the distance between the point electrode and the interface. Finally, an analysis of the observation is performed to show that the Townsend-Meek criterion cannot predict the obtained results.
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| 6. |
- Ariza, David, et al.
(författare)
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Inception of first mode negative streamers at liquid/solid interfaces
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Ingår i: Journal of Physics D: Applied Physics.
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents an experimental study on the inception of first mode negative streamers at different mineral-oil/solid interfaces. This study is performed with a point-plane configuration immersed in mineral oil (point cathode). The mineral-oil/solid interface is done by assembling a solid in an inclined position into the point-plane gap. The solid is in contact (or in the proximity) with the point electrode tip. The tested solids are a kraft paper, a paper made from cellulosic micro and nano fibrils and different polymeric films (low density polyethylene (LDPE), polyethylene terephthalate (PET), polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF)). These solids have different relative permittivity and structural composition. It is found that the streamer inception voltage is statistically similar for the cases with solids with higher permittivity than mineral oil. The streamer inception voltage for the case without any solid barrier is also statistically similar to the cases with solids with higher permittivity than mineral oil. It is also found that the inception voltage is higher for streamers initiated at permittivity-matched interfaces (cases with LDPE and PTFE). Additionally, the influence of the spatial limitation with the solid surface to the volume where the streamer initiation process takes is performed with PTFE by varying the distance between the point electrode and the solid surface. It is shown that the streamer inception voltage depends on the distance between the point electrode and the solid surface. Furthermore, It is observed that the streamer inception voltage is also influenced when the distance between the point electrode and the surface of the PTFE is several micrometers (twenty times longer than the penetration depth of the avalanche responsible of streamer initiation). Additionally, it is also shown that a recently-proposed streamer inception criterion is unsuitable to predict the streamer inception conditions close to permittivity matched and mismatched liquid/solid interfaces.
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| 7. |
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| 8. |
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| 9. |
- Ariza, David, et al.
(författare)
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Influence of Paper Properties on Streamers Creeping in Mineral Oil
- 2017
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Ingår i: Proceedings of IEEE International Conference on Dielectric Liquids. - : IEEE. - 2153-3725 .- 2153-3733.
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Tidskriftsartikel (refereegranskat)abstract
- This work presents an experimental study ofsecond mode positive streamers propagating along mineral oilpaperinterfaces. A point-plane arrangement immersed inmineral oil with the paper inclined 60 degrees to the planeelectrode is used to create the liquid-solid interface. Kraft paperand a kraft fibril paper, made from cellulosic micro and nanofibrils, with higher density and lower surface roughness are usedas the solid materials. High speed shadowgraphy and chargerecordings are used to compare the propagation of second modepositive streamers along the mineral oil-kraft paper and mineraloil-kraft fibril paper. Streamers creeping along the mineral oilkraftpaper interface propagate mainly into the liquid, with oneor two main filaments. In comparison, the streamers propagatingalong the kraft fibril paper show a strong reduction of thebranching; these streamers consist of a single filament thatpropagates exactly on the solid surface. Streamers along the kraftfibril paper also have longer propagation time than for the casewith kraft paper. Mutual electrostatic shielding betweenfilaments is observed for the streamers creeping on the kraftpaper. An electrostatic analysis of the influence of permittivity,density and surface roughness of the solid in the electricalproperties of the streamer filaments is also performed.
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| 10. |
- Ariza, David, et al.
(författare)
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Measurements of the charge of streamers propagating along transformer oil-solid interfaces
- 2014
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Ingår i: Proceedings of the 2014 IEEE 18th International Conference on Dielectric Liquids, ICDL 2014. - : IEEE. - 9781479920631 ; , s. 6893165-
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Konferensbidrag (refereegranskat)abstract
- This paper presents an experimental study of the positive streamer charge in transformer oil and oil-solid interfaces in a point-plane gap (5mm) under impulse voltage 50ns\1800μs (maximum peak voltage 24 kV). The experiment is intended to compare the charge of streamers propagating in transformer oil with and without a solid barrier along their path. The solid barrier constricting the streamer volume consists of two parallel strips of either impregnated pressboard or a polymeric film (PA6) installed at both sides of the point electrode. The maximum cumulative charge of the streamer is found for the case when the impregnated pressboard is used and the minimum cumulative charge for the case of the polymer as a barrier.
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