Σημαντικό ρόλο στις βιομηχανικές εφαρμογές πλάσματος παίζει η ροή των ιόντων. Ωστόσο, συχνά συναντάται το πρόβλημα της εναπόθεσης μονωτικών υμενίων καθιστώντας τους ηλεκτροστατικούς καθετήρες μη λειτουργικούς για τη μέτρηση της ροής αυτής. Ένας εναλλακτικός καθετήρας, ικανός να λειτουργήσει σε αυτές τις συνθήκες, προτάθηκε από τους N. S. J. Braithwaite et al. [1]. Στην παρούσα εργασία παρουσιάζονται, πρώτον, η θεωρία λειτουργίας του καθετήρα αυτού, δεύτερον η κατασκευή του και τρίτον η ανάπτυξη τού συστήματος για την οδήγησή του καθώς και την καταγραφή και την επεξεργασία των σημάτων του. Τέλος, γίνεται πειραματική εξακρίβωση της σωστής λειτουργίας της συσκευής, σε διάταξη επαγωγικού πλάσματος ραδιοσυχνοτήτων (13.56 MHz). / The ion flux holds a major role in the industrial applications of plasma. Often, though, the problem of insulative film deposition is encountered, making the electrostatic probes non functional for the measurement of the ion flux. An alternative probe, capable of functioning under these circumstances has been proposed by N. S. J. Braithwaite et al. [1]. In this paper there are presented, firstly, the theory under which this probe functions, secondly the implementation and thirdly the development of a system for biasing and also data acquisition and processing the signals obtained by the probe. Finally, an experimental identification of the good operation of the device is done, in RF inductively couple plasma (13.56 MHz).

<p>This report presents a model to determine the solar Extreme UltraViolet (EUV) intensity and the ion flux in the vicinity of Saturn, by using measurements from the Langmuir probe, a plasma investigation instrument, of the Cassini satellite. The model is based on in situ measurements and does therefore provide an improved estimation of the wanted parameters compared to previously used calculations based only on the EUV flux measured near Earth. The solar EUV and ion flux were determined by analysing and processing the current measurements from the Cassini Langmuir probe in several steps. Initially the time intervals where the measured current were expected to be due only to the photoelectron current was extracted. The photoelectron current is the part of the measured probe current that is only due to electrons ejected from the probe by photons coming from the Sun. The measurements showed a periodic behaviour which was concluded to be due to the attitude of the satellite. This interfering effect was corrected for and the data was then plotted against an EUV index, estimated from a traditionally used proxy of the EUV flux near Earth; the F10.7 solar radio flux index. In agreement with the theory of the photoelectric effect a linear relationship between the EUV flux and the photoelectron current <em>m_ph</em> was expected. A least square linear fit to the extracted photoelectron current data provided the relation, for the Langmuir probe on Cassini, in the form of the equation <em>m_ph</em>=0.1842<em>EUV</em>+0.2405, where <em>m_ph</em> is the photoelectron current in nA and <em>EUV</em> is the EUV index in W/Hzm^2. The derived equation is the result of the study, showing how to estimate the solar EUV flux using the Langmuir probe current measurements. This result was used to derive the other wanted parameter, the ion flux. The derivation was done by calculating the photoelectron current <em>m_ph </em>at all time and subtracting the result from the total current. The retrieved difference gives the magnitude of the ion current for every measurement.</p>

This report presents a model to determine the solar Extreme UltraViolet (EUV) intensity and the ion flux in the vicinity of Saturn, by using measurements from the Langmuir probe, a plasma investigation instrument, of the Cassini satellite. The model is based on in situ measurements and does therefore provide an improved estimation of the wanted parameters compared to previously used calculations based only on the EUV flux measured near Earth. The solar EUV and ion flux were determined by analysing and processing the current measurements from the Cassini Langmuir probe in several steps. Initially the time intervals where the measured current were expected to be due only to the photoelectron current was extracted. The photoelectron current is the part of the measured probe current that is only due to electrons ejected from the probe by photons coming from the Sun. The measurements showed a periodic behaviour which was concluded to be due to the attitude of the satellite. This interfering effect was corrected for and the data was then plotted against an EUV index, estimated from a traditionally used proxy of the EUV flux near Earth; the F10.7 solar radio flux index. In agreement with the theory of the photoelectric effect a linear relationship between the EUV flux and the photoelectron current mph was expected. A least square linear fit to the extracted photoelectron current data provided the relation, for the Langmuir probe on Cassini, in the form of the equation mph=0.1842EUV+0.2405, where mph is the photoelectron current in nA and EUV is the EUV index in W/Hzm^2. The derived equation is the result of the study, showing how to estimate the solar EUV flux using the Langmuir probe current measurements. This result was used to derive the other wanted parameter, the ion flux. The derivation was done by calculating the photoelectron current mph at all time and subtracting the result from the total current. The retrieved difference gives the magnitude of the ion current for every measurement.

Control of intracellular ion homeostasis is pivotal to plant salt tolerance. Plants have developed a number of mechanisms to keep ions at appropriate concentrations. Both transporters and channels on the plasma membrane play important roles in this function. Plant cyclic nucleotide-gated channels (CNGCs) in the plasma membrane are non-selective monovalent and divalent cation channels. So far, most studies on plant CNGCs have been conducted on heterologous systems. In planta, reverse genetic studies revealed the role of different CNGCs in cation uptake, transport and homeostasis. However, there is little information available about the functional characteristics of plant CNGCs. Among the 20 members of this protein family in Arabidopsis, only AtCNGC2 has been functionally identified as an ion channel; therefore, more functional characterization needs to be done on other members of this protein family. Several CNGCs were suggested to be involved in K+, Ca2+ and Na+ uptake and transport, but available information is scarce. This study investigated the relationship between CNGC10 and ion transport in Arabidopsis, with a particular emphasis on the involvement of CNGC10 in salt tolerance. Arabidopsis thaliana wild type (WT) and two AtCNGC10 antisense lines (A2 and A3) were used to characterise the impact of different level of salt stress on (i) root growth, ion concentration in tissues, ion fluxes across the root surface and intracellular ion concentration and pH at the seedling stage, and (ii) photosynthesis and ion concentration in tissues at the flowering stage. Plants of both antisense lines had higher K+ and lower Ca2+ and Mg2+ concentrations in shoots than WT plants when grown in non-salt control 1/4 Hoagland solution. Altered K+, Ca2+ and Mg2+ internal concentrations in AtCNGC10 antisense lines compared with WT plants under non-salt conditions indicated disturbed long distance ion transport, especially xylem loading/retrieval and/or phloem loading. The results of ion fluxes across the root surface also suggested that AtCNGC10 might be involved in transport of K+, Ca2+ and Mg2+ in tissue. Under sudden salt exposure, higher Na+ efflux and smaller K+ efflux in both antisense lines suggested that AtCNGC10 channels are involved in Na+ and K+ transport. The shoots of AtCNGC10 antisense lines A2 and A3 contained higher Na+ concentrations and significantly higher Na+/K+ ratios compared to WT, resulting in impaired photosynthesis and increased salt sensitivity in A2 and A3 than in WT plants. In contrast, seedlings of both antisense lines exposed to salt stress had lower shoot Na+/K+ ratios and longer roots than WT seedlings, indicating that A2 and A3 were more salt-tolerant than WT in the seedling stage, likely because growth is less dependent on photosynthesis in the seedling than in the flowering stage. These results suggested CNGC gene might play a different role during different developmental stages and in various plant organs.

Black Cottonwood (Populus trichocarpa) is a fast-growing, economically important tree species. P. trichocarpa was the first tree to have its genome fully sequenced and is considered the model organism for genomic research in trees. Of the macronutrients in plants, Nitrogen (N) is required in the greatest amounts and is generally the limiting nutrient in terrestrial ecosystems. Inorganic N-transport is performed by four families of transporter proteins, AMT1 and AMT2 for ammonium (NH4+) and NRT1 and NRT2 for nitrate (NO3-). I have created phylogenetic reconstructions of each of these transporter families in 22 members of Viridiplantae whose genomes have been fully sequenced. Based on these phylogenies, I have introduced a new classification system for the transporter families that better represents the evolutionary and functional relatedness of the proteins. These phylogenies were supplemented with topology predictions, subcellular localization predictions, and in silico expression profiling in order to suggest functional characterization of the groups. This facilitated candidate gene selection for NH4+ and NO3- uptake transporters from P. trichocarpa. Expression profiling was performed on two of these candidates. Results suggest that PtAMT1-1 may be a high-affinity, root-localized NH4+ transporter. In contrast, PtNRT2-6 is a high-affinity NO3- transporter localized to the dormant bud, but its physiological functions remain largely enigmatic. Flux profiles of NH4+, NO3-, and H+ in the first 1.4 cm of root tips of three-week-old P. trichocarpa seedlings and cuttings were measured using the Microelectrode Ion Flux mEasurement (MIFE) system to demonstrate the activity of AMTs and NRTs under nutrient-abundant and nutrient-deficient conditions. I found mainly N-efflux from roots of cuttings while seedling roots exhibited N-uptake. This is the first report of such a difference. This highlights an unexpected but clear physiological difference between seedling and cutting roots, which are frequently used in experimental setups. / Graduate / 0817 / 0369 / 0715 / neilvonw@gmail.com

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