Caracterización morfológica de la semilla de Hibiscus cannabinus (Malvaceae) e influencia del tiempo de almacenamiento sobre la viabilidad

Hibiscus cannabinus L. (Malvaceae) “kenaf ” es una especie de ciclo anual primavero-otoñal, que se cultiva para la producción de fibra para papel, bioetanol de segunda generación y forraje. Los objetivos de esta investigación fueron caracterizar la morfología de la semilla de H. cannabinus y establecer la influencia del tiempo de almacenamiento sobre la viabilidad de dos cultivares, Endora y Tainung 1. Se realizaron observaciones de cortes histológicos y mediciones con microscopio óptico y estereoscópico. Se evaluó la germinación a los 30, 180 y 730 días después de cosecha. Las semillas de H. cannabinus presentan una forma asimétrica, cuneiforme y/o triangular (ca. 5,1 mm x 2,8 mm), son endospermadas y derivan de óvulos campilótropos. La cubierta seminal tiene tricomas unicelulares, eglandulares distribuidos en toda la superficie con predominio en la región del hilo. El embrión es plegado, con cotiledones conduplicados de posición axial sub tipo curvo. El episperma presenta un marcado predominio de la capa de macroesclereidas. Se encontró que las semillas de los cultivares Endora y Tainung 1, almacenadas por dos años a temperatura ambiente y con 9,5% de humedad, mantienen un alto porcentaje de germinación con valores cercanos al 80%. Los resultados permiten afirmar que las semillas de “kenaf ” mantienen las características morfológicas internas constantes típicas de las Malváceas, y que los cultivares estudiados presentan una alta viabilidad sostenida en el tiempo

Evaluación de dos fechas de siembra de Hibiscus cannabinus L. 'kenaf' (Malvaceae) en Villa del Totoral, Córdoba, Argentina

31-42El objetivo de este trabajo fue evaluar el rendimiento de fibra del cultivo de 'kenaf'en dos fechas de siembra en Villa del Totoral, Córdoba, Argentina. Se analizaron: altura de planta durante el ciclo del cultivo; diámetro basal y medio del tallo y altura a cosecha; rendimiento de fibra y contenido e índice de corteza. Se observó interacción altamente significativa entre año y fecha de siembra. En el primer año, las plantas de la siembra temprana presentaron mayores valores de altura, diámetro basal y medio y rendimiento, que las de la siembra tardía. Por el contrario en el segundo año, sólo se encontraron diferencias significativas entre fechas de siembra para ambos diámetros. El rendimiento correlacionó con altura, diámetros e índice de corteza y no con el contenido de corteza. Se sostiene que para obtener alto rendimiento de fibra de 'kenaf' en las condiciones ambientales del ensayo, es conveniente la siembra al inicio de la temporada de lluvias sin embargo, dependiendo de las condiciones ambientales, se puede esperar hasta fines de noviembre sin detrimento en los rendimientos

The power of monitoring: optimizing survey designs to detect occupancy changes in a rare amphibian population

Biodiversity conservation requires reliable species assessments and rigorously designed surveys. However, determining the survey effort required to reliably detect population change can be challenging for rare, cryptic and elusive species. We used a tropical bromeliad-dwelling frog as a model system to explore a cost-effective sampling design that optimizes the chances of detecting a population decline. Relatively few sampling visits were needed to estimate occupancy and detectability with good precision, and to detect a 30% change in occupancy with 80% power. Detectability was influenced by observer expertise, which therefore also had an effect on the sampling design – less experienced observers require more sampling visits to detect the species. Even when the sampling design provides precise parameter estimates, only moderate to large changes in occupancy will be detected with reliable power. Detecting a population change of 15% or less requires a large number of sites to be surveyed, which might be unachievable for range-restricted species occurring at relatively few sites. Unless there is high initial occupancy, rare and cryptic species will be particularly challenging when it comes to detecting small population changes. This may be a particular issue for long-term monitoring of amphibians which often display low detectability and wide natural fluctuations

LiNbO3_{\bf 3}-based ferroelectric heterostructures

We report the growth of LiNbO$_{3}$ thin films onto In$_{2}$O$_{3}$:Sn-coated $\langle$111$\rangle$-Si substrates by standard radio-frequency sputtering. Multi-layer procedures, up to 4 successive deposits, have been developed that can subsequently improve the structural and macroscopic ferroelectric properties of such as-grown composite structures. The enhancement of polarization, as high as 40 $\mu$C.cm$^{\hbox{-}2}$ in 4 stacked layers, is attributed to $c$-oriented seed-layer-induced crystallization (self-polarization) and interfacial (migratory) polarizatio

ITO-based electrode: A promising candidate for the growth of piezoelectric thin films

In many ways, interfaces and surfaces dominate the behavior of thin films and multilayered devices. The critical nature that the interfaces play on numerous physical properties has stimulated significant effort to both understand such behavior and develop novel and potentially useful nanoscale systems. In particular, the use of suitable buffer layers has been shown to allow the control of nucleation and growth processes and, thus, the fabrication of a very wide range of nanostructured materials. This paper briefly overviews the relevant experimental work performed at the LPMC and related to piezoelectric thin films. Particular emphasis is given to In$_{2}$O$_{3}$:Sn oxide as an interesting conductive electrode / buffer layer for the growth of various piezoelectric compounds including LiNbO$_{3}$ (LN), Pb(Zr$_{0,52}$Ti$_{0,48})$O$_{3}$ (PZT), ZnO

Hormographiella aspergillata keratomycosis in a dog

A 4-year-old, female, Border Collie was presented to the University of Bern Veterinary Teaching Hospital, because of a corneal lesion of 10 days duration. The axial cornea presented a whitish fluorescein-positive plaque with irregular margins. A diagnosis of keratomycosis was made based on cytology. Medical therapy with local broad-spectrum antibiotic and fluconazole was instituted. After 1 week of treatment, the improvement was deemed unsatisfactory. Therefore, a lamellar keratectomy and conjunctival pedicle flap were performed. After surgery, the cornea healed uneventfully. Histology confirmed the diagnosis of keratomycosis. The fungus could not be grown in culture and a precise etiological diagnosis could only be obtained with genetic identification of the fungus. A PCR technique was used to amplify the fungal genome from the cornea. Hormographiella aspergillata, the asexual reproductive form of the basidiomycete Coprinopsis cinerea, was identified. As advised in human medicine, we encourage the use of this molecular technique to obtain an early species diagnosis, allowing targeted medical therapy

Propriétés diélectriques et piézoélectriques de céramiques de Pb(Mg1/3_{1/3}Nb2/3_{2/3}O3_{3} – PbTiO3_{3} dopées

0.65 Pb(Mg$_{1/3}$Nb$_{2/3}$)O$_{3}$ – 0.35 PbTiO$_{3}$ ceramics doped with lanthanum, iron and manganese oxides were synthesized. Experimental results showed the dopants by creating some points defects in the network of PMN-PT act on the microstructural development of ceramics and as a result on to dielectric constant and losses values. Moreover when the Mn$^{+4}$ ion were used as a dopant in a B site of the network, dielectrics losses were notably decreased allowing some using of this material in the field of acoustic wave at reasonable power.Différentes céramiques de composition 0,65 Pb(Mg$_{1/3}$Nb$_{2/3}$)O$_{3}$ – 0,35 PbTiO$_{3}$ (PMN-PT) dopées avec des oxydes de lanthane, de fer et de manganèse ont été synthétisées sous forme de composés massifs. Il ressort de cette étude que les dopants, en introduisant des défauts ponctuels dans le réseau, agissent sur la microstructure des céramiques et conditionnent ainsi les valeurs de la constante diélectrique et des pertes. L'ion Manganèse Mn$^{4+}$ en substitution dans les sites B de la structure des PMN-PT (35 % PT) permet d'abaisser de manière importante les pertes diélectriques du matériau, ce qui pourrait permettre d'utiliser cette céramique pour des applications de moyenne puissance

Influence des paramètres de dépôt sur la morphologie de films minces de tétraborate de lithium obtenus par le procédé “PYROSOL"

Li$_2$B$_4$O$_7$ piezo-electric thin films were prepared by “PYROSOL" process which is a useful method for the elaboration of thin films. Morphological development and crystallization of thin films are very dependent on the experimental parameters like the substrate temperature, the concentration and the relative proportion of the precursors in methyl alcohol. The effect of these various parameters were studied in order to obtain homogeneous, crystallized and oriented thin films.La réalisation de couches minces de matériaux piézo-électriques de Li$_2$B$_4$O$_7$ par le procédé “PYROSOL" révèle une grande diversité de conditions de dépôt. La température du substrat, la composition des solutions de précurseurs et leur concentration conditionnent la morphologie et l'état de cristallisation des films. En particulier, l'obtention de couches minces denses, homogènes et présentant une orientation préférentielle nécessite des températures de substrat supérieures à 620 $^{\circ}$C. L'influence de ces divers paramètres expérimentaux a été étudiée dans le but d'obtenir des dépôts homogènes, cristallisés et orientés