ALBERT

Notes: During the last decade, there has been an increasing use of synchrotron x-ray techniques for the in situ investigation of the structure and composition of metal/solution interfaces under electrochemical control. While a number of experimental cell designs have been utilized in the past, every one of them has exhibited some shortcomings. This paper describes the development of a wide-angle-accessible, transmission-geometry, sandwich-type, x-ray/electrochemical cell. From an x-ray physics standpoint, this cell allows uninterrupted access over a 180° in-plane angle for all incident and scattering angles between 0° and 75° with respect to the sample surface. It is especially advantageous at small scattering angles because of the uniform and insignificant background scattering. From an electrochemical standpoint, this cell provides a uniform current distribution and continuous, precise potential control of the working-electrode surface; at the same time, it permits easy flushing of the working solution and even accommodates operating with flowing solution. Its only disadvantage is its inability to permit in situ cyclic voltammetry of only one surface of the single crystal.

Notes: An experimental system for studying acoustic signals generated by a modulated MeV ion beam in metals is described. For detection, a closed cell on the rear side of a copper or aluminum sample, a half-inch condenser microphone, and a lock-in amplifier were employed. The pressure signal was found to be proportional to beam current and particle energy, and inversely proportional to cell length. Decrease of the signal magnitude and increase of the phase delay with increasing modulation frequency and sample thickness were also observed.

Notes: Electrochemical oxidation causes the lifting of Pt atoms of the surface layer, substantiating a place-exchange mechanism. Furthermore, for a charge transfer of (approximately-less-than)1.7e−/Pt atom, the flat surface is recovered by reduction, while the surface is irreversibly roughened by more excessive oxidation. Roughening involves only the atoms in the top layer.

Notes: Theoretical studies have shown the possibility of high-temperature (‘high enthalpy’) geothermal reservoirs in the pre-Tertiary rocks at 4–5 km depth range within the Pannonian Basin. This expectation was proven by the hotwater/steam blowout of Fábiánsebestyén-4 borehole (16.12.85–31.1.86). Exploration efforts carried out during 1987–88 in the broad vicinity of the borehole proved that reservoirs of this type can be found with the combination of seismic reflection, silica-thermometry and magnetotelluric sounding methods. Deliberate prospection should be continued in all suitable areas within the basin, since high enthalpy reservoirs promise profitable operation of geothermal power stations.

Notes: Interspecific competition between Amaranthus chlorostachys Willd. and sunflower (Helianthus annuus L., NSH-33 hybrid) in pure and mixed stands of the same density was studied in small plot experiments to elucidate the ecophysiological responses of the competing species under drought stress.When grown in a mixed stand the extremely low intensity of transpiration in A. chlorostachys resulted in a difference in the water use efficiency (WUE) values of net photosynthesis between the two species. The values were higher in A. chlorostachys. Interspecific competition reduced the total individual plant weight to a greater extent in sunflower than in the weed species by the end of the growing season. Reproductive effort was higher in A. chlorostachys than sunflower and, in our opinion, best reflects the outcome of competi-tion. On the basis of the correlation between WUE and reproductive allocation, reproduc-tive effort in sunflower and A. chlorostachys in both intra- and interspecific competition is determined by the value of WUE, which latter is also of prime importance in drought stress tolerance. Approche écophysiologique de la compétition entre Amaranthus chlorostachys et le tournesol (Helianthus annuus) en condition de stress hydriqueLa compétition interspécifique entre Amaranthus chlorostachys Willd. et le tournesol (Helianthus annuus L. hybride NSH 33) dans des stations mixtes et simples de densité de plantes identiques (espacement de 35 × 35 cm) a étéétudié dans une expérimentation de plein champ en petites parcelles. Notre but était d'éclairer les réponses écophysiologiques des espèces en compétition (compétition inter et intra spécifique) sous stress hydrique et de mettre en lumière les corrélations entre les processus ecophysiologiques adéquats et les paramètres de la production de biomasse quan-tifiant le résultat de la compétition.Quand la culture a été faite dans des stations mixtes, la très faible intensité de transpiration chez A. chlorostachys a abouti à une différence ultérieure entre les valeurs de l'efficacité de l'utilisation (WVE) de l'eau dans la photosynthèse chez les 2 espèces: celle-ci était plus élevée chez A. chlorostachys. La compétition interspécifique a réduit le poids total des plantes individuelles de faon plus importante chez le tournesol que chez la mauvaise herbe à la fin de la saison de croissance. L'importance de la reproduction, qui à notre avis reflète le mieux le résultat de la compétition exprimée dans une aptitude à se reproduire plus élevée chez A. chlorostachys que chez le tournesol.Sur la base de la corrélation entre WVE et l'aptitude à se reproduire, l'importance de la reproduction chez le tournesol et A. chlorostachysà la fois en compétition intra et inter spécifique est déterminée par la valeur de WVE, qui est aussi de première importance dans la tolérance au stress hydrique. Ökophysiologische Untersuchung der Konkurrenz zwischen Amaranthus chlorostachys und Sonnenblume (Helianthus annuus) unter TrockenstreβDie Konkurrenz zwischen Amaranthus chlorostachys Willd. und der Sonnenblume (Helianthus annuus L., ‘NSH-33’) in Rein- und Mischbeständen gleicher Pflanzendichte (Abstand 35 cm) wurde in Feldversuchen auf kleinen Parzellen untersucht. Die ökophysiologische Reaktion der konkurrierenden Arten (bei intra- und interspezifischer Konkurrenz) unter Trockenstreß, die Beziehungen zwischen den relevanten ökophysiologischen Prozessen und die Biomasseproduktion unter dem Einfluß der Konkurrenz sollten bestimmt werden. In Mischbeständen führte die extrem niedrige Intensität der Transpiration von Amaranthus chlorostachys zu einer noch verstärkten Differenz zwischen den Werten der Wasserausnutzung (WUE) der Netto-Photosynthese der beiden Arten, die bei Amaranthus chlorostachys höher waren. Die interspezifische Konkurrenz verringerte die Einzelpflanzenmasse bei der Sonnenblume zum Ende der Vegetationsperiode stärker als beim Unkraut. Der Repro-duktions-Aufwand, der unserer Meinung nach die Konkurrenzwirkung am besten widerspiegelt, war bei Amaranthus chlorostachys höher als bei der Sonnenblume. Er wird bei beiden Arten sowohl bei intra- als auch interspezifischer Konkurrenz durch den Wert der WUE bestimmt, die auch für die Trockenstreß-Toleranz sehr wichtig ist.