La Ciudad y los campos : semanario de acción nacional: Año III Número 61 - 04 Marzo 1933

Copia digital. Madrid : Ministerio de Cultura. Subdirección General de Coordinación Bibliotecaria, 200

The role of water in the conductivity of vanadium pentoxide xerogel films

The measurement of DC conductivity of thin films deposited from vanadium pentoxide gels between 200 and 600 K in air, oxygen and a vacuum of 5 x 10 -7 torr has revealed that reversible changes in conductivity are determined by hydration/dehydration phenomena. The removal of weakly bonded water results in a conductivity decrease from ≃ 2 S/m to ≃ 0.3 S/m at room temperature. Heat treatment between 430 and 550 K in oxygen leads to the maximally dehydrated phase in which σ ≃ 9 × 10-3 S/m at 300 K. The essentially unchanged activation energies in all of the phases suggest that hydration affects the charge carrier concentration only.Nous avons mesuré entre 200 et 600 K la conductivité à l'air libre ou sous un vide de 5 x 10-7 torr, de couches minces obtenues à partir de gels de pentoxydes de vanadium. Ces mesures ont montré que les changements réversibles de la conductivité sont liés à des phénomènes d'hydratation et de déshydratation. Le départ de l'eau faiblement absorbée entraîne, à température ambiante, une diminution de la conductivité de ≃ 2 S/m à 0,3 S/m. Un traitement thermique entre 430 et 550 K dans une atmosphère d'oxygène conduit à une phase de déshydratation maximum avec σ ≃ 9 x 10-3 S/m à 300 K. Le fait que les énergies d'activation sont similaires dans les différentes phases suggère que le processus d'hydratation entraîne seulement une modification de la concentration des porteurs de charge

Fire blight (Erwinia amylovora) susceptibility of old Hungarian apple cultivars

The aim of the Hungarian apple breeding program started in the Department of Fruit Science was to find resistant apple cultivars against major diseases (scab, powdery mildew, fire blight). The outbreak of fire blight (Erwinia amylovora) in 1996 motivated us to search new resistant sources principally from old traditional apple cultivars. First of all, cultivars have been gathered since 1997 from Carpathia (Visk) and evaluated between 2001 and 2003. In this recent study evaluation of resistance of old Hungarian genotypes to fire blight collected from the English National Fruit Collection (Brogdale, Faversham) is presented. 13 old Hungarian apple cultivars in 2002, and 38 genotypes in 2005 have been evaluated. We used `Idared' and 'Jonathan M41' as susceptible controls and 'Liberty' and 'Remo' as resistant ones. Shoots of two-year-old potted plants were inoculated with a mixture of virulent E. amylovora isolates (Ea2, Ea60, Ea67) at a concentration of 5 x 108 cells/ml. Resistance of apple cultivars was evaluated weekly, four times after inoculation by disease severity of symptoms. Numbers of bacterial colonies in 1 cm length shoot were determined in the fourth week after infection. 8 cultivars in 2002 and 9 cultivars in 2005 displayed notable resistance to fire blight based on one-year data. Based on the coincident data of both years, out of the cultivars collected also from Carpathia ‘Pónyik', and `Sikulai' were found to be resistant and gene sources additional old Hungarian valuable apple genotypes could be selected: `Szabadkai szercsika' and `Tordai piros !davit'. The cultivar `Szemes alma' originated from Visk has proved to be recurrently resistant. The number of bacterial cells in shoots of the investigated cultivars correlated with the severity of symptoms. With this method, which was introduced by us earlier, we can screen cultivars displaying weak visible symptoms, which cannot be proposed as a source of resistance because of their latent infection

Historical apple cultivars that display high level of resistance to fire blight

Following the first outbreak of fire blight caused by the bacterium Erwinia amylovora (Burrill) Winslow et al. in Hungary, we have started research with the aim to screen domestic gene sources, mostly historical Hungarian apple cultivars, for disease resistance as part of an apple breeding program for multiple resistance. The present study was conducted with the aim to choose the most tolerant historical apple cultivars among 25 selected cultivars by screening their behavior towards fire blight under controlled conditions. Six cultivars were shown to be the most disease tolerant: `Batul', 'London pepin', Nemes Sóvári Alma', `Sikulai', `Szemes alma', Wilmos renet'. We evaluated these cultivars by investigating both morphological- characteristics under original environmental circumstances and fruit quality. The cultivars had a remarkable degree of fire blight resistance compared to the control cultivars. These were not competitive with the commercially grown 'Jonathan M40' during cultivar tests but on the basis of certain characteristics they could serve as genetic sources for breeding new varieties

Historical apple cultivars that display high level of resistance to fire blight

Following the first outbreak of fire blight caused by the bacterium Erwinia amylovora (Burrill) Winslow et al. in Hungary, we have started research with the aim to screen domestic gene sources, mostly historical Hungarian apple cultivars, for disease resistance as part of an apple breeding program for multiple resistance. The present study was conducted with the aim to choose the most tolerant historical apple cultivars among 25 selected cultivars by screening their behavior towards fire blight under controlled conditions. Six cultivars were shown to be the most disease tolerant: `Batul', 'London pepin', Nemes Sóvári Alma', `Sikulai', `Szemes alma', Wilmos renet'. We evaluated these cultivars by investigating both morphological- characteristics under original environmental circumstances and fruit quality. The cultivars had a remarkable degree of fire blight resistance compared to the control cultivars. These were not competitive with the commercially grown 'Jonathan M40' during cultivar tests but on the basis of certain characteristics they could serve as genetic sources for breeding new varieties

AMORPHOUS VANADIUM OXIDES BY CVD : PREPARATION, ELECTRICAL AND MAGNETIC PROPERTIES

Chemical vapour deposition of VOCl3 with H2O in controlled atmosphere is a unique method in producing amorphous vanadium oxides that contain only V5+ and V4+ ions with continuously varying valence ratio /c/ between <0.02 and ≈ 1.0. The room temperature d.c. conductivity of as prepared V2O5 films ranges between 10-5 and 10-3 ohm-1m-1 and is strongly dependent on preparation conditions. Increasing the valence ratio the conductivity first increases to ≈ 10-2 ohm-lm-1, then declines to 10-4 ohm-lm-1. EPR spectra indicate that the environment of V4+ ions is not identical in films of different compositions