The method described herein permitted production of three to four micropropagules of Acacia Senegal from one uninodal explant. The explants were taken from plants produced either in a sterile environment or during four years in a greenhouse. Zeatin or 6-benzylaminopurine (BAP) were mixed, at different concentrations, with Murashige and Skoog's medium (MS) of which the amount of macroelements was divided in half (MS mod.). At a concentration of 5.0×10(-5) M, zeatin produced a better multiplication rate after 60 d for the two types of plant stock than did BAP. A two stage process was necessary to obtain a rooting rate of the small cuttings close to 100%. The first stage, called induction, consisted of leaving the cuttings for 6 to 12 d on a Jordan's medium (JN) of which the amount of macroelements was reduced by half (JN mod.) and in which NAA at a concentration of 5.0×10(-5) M was added. The second stage, called root extension, required that the small cuttings be planted on this second hormone-free medium. Roots appeared after a few days. Acclimatization in a greenhouse occured with a survival rate of close to 100% when the rooted in vitro plants were transplanted to pots containing a mixture of vermiculite and top soil (1∶1; v/v).
This paper presents the results of fundamental investigations on the inception and propagation of corona discharge on an ice surface stressed with a standard lightning impulse voltage. High-speed photography and photomultiplier techniques were used to observe and record the propagation of the streamers. The effects of several experimental parameters such as freezing water conductivity and HV rod electrode radius on the streamer inception parameters were investigated. Moreover, time to first streamer, inception voltage and corresponding field, as well as streamer propagation velocity and charge deposited by a streamer on ice surface were measured. The results are discussed and emphases are laid on the main factors influencing the development of positive streamers on ice surface.Index Terms -Outdoor insulation, atmospheric icing, ice surface, high-speed camera, streamer inception, streamer propagation velocity, surface charge, flashover.
The global mechanical properties of composite structures in service depend on fiber/matrix interface and interlaminar strength. The paper proposes to use Acoustic Emission (AE) and advanced signal processing to evaluate the interlamnar performance of polymeric composites. A delaminating process simulated with a Double Cantilever Beam (DCB) in opening mode (Mode I) coupled with a n Acoustic Emission (AE) technique has been employed. Different samples were analyzed to observe the damage evolution and to evaluate the interlaminar decohesion processes. The resistance to delamination growth is expressed in terms of the interlaminar DCB mode (mode I) fracture toughness, measured by strain energy release rate, GI, dissipated per unit area of delamination growth in composite. Three categories of samples were used: two unidirectional carbon fiber/epoxy resins with one degraded by heat and one with a commercially used resin. It was found that sample that was exposed at a temperature greater than the glass transition temperature Tg of the epoxy had a higher cumulative energy release rate than the two other samples types. The original type having the lowest release rate. Acoustic emission parameters have been found to be powerful indicators of the intensity of the damage. Multivariate analysis of up to 49 parameters was performed in order to group classes of AE signals with matching characteristics. A correlation was established between the energy release rate and the acoustic emission energy.
In order to study and monitor rates of rooting, callusing and survival, small diameter stem cuttings (less than 0.4 cm) with eight nodes (12--14 cm long) were taken from trees in the field at different times of the year in tests with small batches of cuttings. Among the four tested substrates, well drained crushed basalt powder placed on a bed of gravel was the best rooting medium. Rooting was generally poor or even non-existent with this type of cutting, but the presence of leaves both promoted rooting and significantly (using Chi square test) improved survival of the cutting. Four leaves were sufficient to assure the necessary metabolic functions. Only stem cuttings collected during the rainy season gave roots and then, only when hormonal treatments were applied to the cuttings. 8%-IBA resulted in significantly better rooting than did 2%-IBA, 0.2%-NAA and I%-IAA. With 8%-IBA, the rate of rooting varied between 50 and 70% for leafy cuttings collected in the rainy season. Hormonal treatments had a significant effect on the survival rate of the stem cuttings during the two months observation period. Further investigations are being conducted with different types of cuttings.Resum& Des boutures de huit noeuds (12 fi 14 cm de long) et de faible diam6tre (inf6rieur 0.4 cm) ont ~t6 pr61ev6es au champ, sur des arbres adultes, h diverses p6riodes de l'ann6e en vue d'6tudier leurs taux d'enracinement, de formation de cals et de survie. La poudre de basalte concass6e sur lit de gravier, avec un bon drainage, s'est r6v616e comme le meilleur substrat. Avec ce type de bouture, la pr6sence de feuilles parait absolument indispensable pour obtenir un enracinement. Quatre feuilles sont suffisantes pour assurer le r61e trophique qui est probablement le leur. La n6o-formation de racines n'est apparue que sur les boutures pr61ev6es durant la saison des pluies. Sans traitement hormonal les boutures du type 6tudi6 n'ont donn6 aucun r6sultat. L'AIB-8% en poudre se r6vble meilleur que I'AIB-2%, I'ANA-0.2% et I'AIA-I%. Avec I'AIB-8%, les taux d'enracinement vont de 50 fi 70% si le substrat, I'hygrom6trie, la pr6sence de feuilles et la p6riode de pr~16vement sont convenables.
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