Portable Apparatus for Electrochemical Sensing of Ethylene

A small, lightweight, portable apparatus based on an electrochemical sensing principle has been developed for monitoring low concentrations of ethylene in air. Ethylene has long been known to be produced by plants and to stimulate the growth and other aspects of the development of plants (including, notably, ripening of fruits and vegetables), even at concentrations as low as tens of parts per billion (ppb). The effects are magnified in plant-growth and -storage chambers wherein ethylene can accumulate. There is increasing recognition in agriculture and related industries that it is desirable to monitor and control ethylene concentrations in order to optimize the growth, storage, and ripening of plant products. Hence, there are numerous potential uses for the present apparatus in conjunction with equipment for controlling ethylene concentrations. The ethylene sensor is of a thick-film type with a design optimized for a low detection limit. The sensor includes a noble metal sensing electrode on a chip and a hydrated solid-electrolyte membrane that is held in contact with the chip. Also located on the sensor chip are a counter electrode and a reference electrode. The sensing electrode is held at a fixed potential versus the reference electrode. Detection takes place at active-triple-point areas where the sensing electrode, electrolyte, and sample gas meet. These areas are formed by cutting openings in the electrolyte membrane. The electrode current generated from electrochemical oxidation of ethylene at the active triple points is proportional to the concentration of ethylene. An additional film of the solid-electrolyte membrane material is deposited on the sensing electrode to increase the effective triple-point areas and thereby enhance the detection signal. The sensor chip is placed in a holder that is part of a polycarbonate housing. When fully assembled, the housing holds the solid-electrolyte membrane in contact with the chip (see figure). The housing includes a water reservoir for keeping the solid-electrolyte membrane hydrated. The housing also includes flow channels for circulating a sample stream of air over the chip: ethylene is brought to the sensing surface predominately by convection in this sample stream. The sample stream is generated by a built-in sampling pump. The forced circulation of sample air contributes to the attainment of a low detection limit

L’Arménie et Byzance

Le voisinage étroit et ancien du monde arménien et de l’Empire byzantin a multiplié entre eux les liens, et il y a longtemps déjà que les divers domaines où se sont manifestés ces contacts font l’objet d’études. Si les Arméniens étaient attentifs à leur indépendance religieuse, ils n’en furent pas moins séduits par le prestige diplomatique et culturel de l’Empire. Quant aux Byzantins, ils appréciaient les guerriers en quête de fortune, qui, longtemps, les protégèrent de l’avance musulmane. Ces sentiments complexes ont perduré, en se transformant, à travers tous les bouleversements du Proche Orient : expansion arabe des viie-viiie siècles, impérialisme byzantin des xe-xie, et avance turque des xie-xiie. À l’heure où l’attention se porte aussi sur les différences et incompatibilités entre Arméniens et Byzantins, le moment était venu pour des historiens d’Arménie, de Russie, des États-Unis et de France, de se rencontrer et de poser les bases d’un bilan sur ces relations contrastées. On trouvera donc ici les contributions de S. S. Arevsatyan, Viada Arutjunova-Fidanjan, Hratch Bartikian, Paul Bellier, Patricia Boisson-Chenorhokian, Isabelle Brousselle, Marie-Louise Chaumont, Jean-Claude Cheynet, Gérard Dédéyan, Patrick Donabédian, Nina G. Garsoïan, Mourad Hasrat’yan, Jean-Pierre Mahé, Seiranouche Manoukian, Bernadette Martin-Hisard, Petre S. Nasturel, Catherine Otten-Froux, Bernard Outtier, Charles Renoux, Michel Thierry, Nicole Thierry et Karen Yuzbashian