Bibliothek

Notizen: Room temperature distributed-feedback (DFB) laser operation is demonstrated with emission wavelengths ranging from 389 to 399 nm. Second-order DFB gratings were defined by electron beam lithography and reactive ion etching in the top GaN barrier layer of a GaInN/GaN double heterostructure grown by metalorganic vapor phase epitaxy. Our data allow a precise determination of the effective refractive index neff(λ) over the whole emission range. neff(λ) is compared with previously published values for GaN and GaInN. © 1996 American Institute of Physics.

Notizen: We measured the Ca2 red system using filtered laser excitation to simplify the spectrum. The transition is assigned A 1Σ+u −X 1Σ+g, where X is the previously studied van der Waals ground state and A correlates adiabatically to 1S+1D calcium atoms. The A state suffers many homogeneous and heterogeneous perturbations, which are assigned to interactions with components of c 3Πu. Following deperturbation of the band spectra, we find that the A state dissociation energy, D'e is 8694±2 cm−1, with a vibrational frequency, ωe, of 126.73±0.11 cm−1, and an equilibrium internuclear separation, Re, of 3.63 A(ring). The analysis shows c 3Πu, which correlates to 1S+3P atoms, is bound by at least 1170 cm−1, with ωe≥67.7 cm−1 and Re≤4.25 A(ring). The assignment of the previously analyzed green system of Ca2 is revised to B 1Σ+u– X 1Σ+g, where B correlates adiabatically to 1S+1P atoms. The new assignment gives B a dissociation energy of 5783 cm−1, and resolves some confusion about the origin of the Ca2 red and green systems.

Notizen: White clover (Trifolium repens L.) is experiencing increased levels of ultraviolet-B (UV-B) radiation in temperate pastures due to the depletion of the stratospheric ozone layer. Based on 17 morphological, morphogenetic and physiological attributes, this study analysed the consequences of enhanced UV-B on 26 white clover populations using principal components analysis (PCA). After 18 d of exposure to 13·3 kJ m−2 d−1 UV-B in controlled environments, UV-B significantly decreased above-ground and below-ground plant growth attributes, epidermal cell surface area and maximum quantum efficiency of photosystem II photochemistry (Fv/Fm). Aspects of cell division and cell expansion both were negatively affected by UV-B. Stomatal density, specific leaf mass, root-to-shoot ratio and levels of UV-B-absorbing compounds increased in response to UV-B. In the multivariate analysis, the main dimension of UV-B sensitivity was characterized by changes in plant growth attributes. Alterations in partitioning within and between plant organs constituted a secondary tier of UV-B responsiveness. Plant characteristics related to UV-B tolerance included lower growth rate, smaller epidermal cell surface area and higher UV-B-induced levels of UV-B-absorbing compounds. The results suggest overall UV-B tolerance for slower-growing populations from less productive habitats with higher natural UV-B irradiance.

Notizen: This study used comparisons across nine populations of Trifolium repens (white clover) in conjunction with drought to examine physiological responses to ultraviolet-B radiation (UV-B). Plants were exposed for 12 weeks to supplementation with 13.3 kJ m−2 d−1 UV-B, accompanied by 4 weeks of drought under controlled environmental conditions. UV-B increased the levels of UV-B-absorbing compounds and of flavonol glycosides and this effect was synergistically enhanced by water stress. These changes were more pronounced for the ortho-dihydroxylated quercetin, rather than the monohydroxylated kaempferol glycosides. UV-B increased leaf water potential (ψL) by 16% under drought and proline levels by 23% under well-watered conditions. The intraspecific comparisons showed that higher UV-B-induced levels of UV-B-absorbing compounds, of quercetin glycosides and of ψL were linked to lower plant productivity and to higher UV-B tolerance under well-watered conditions. These findings suggest that: (1) slow-growing T. repens ecotypes adapted to other stresses have higher capacity for physiological acclimation to UV-B; and (2) that these attributes also contribute to decreased UV-B sensitivity under drought.

Notizen: Die äußere Morphologie und die Topographie einschließlich Röntgen-anatomie der Bauchorgane und ihre Funktionsstadien wurden an 10 Rehen untersucht (liegend oder stehend formalinfixiert).Der Grundbauplan anderer Wiederkäuer ist gewahrt, unterscheidet sich aber deutlich durch gruppenspezifische Merkmale von denen der grasfressenden Hauswiederkäuer Rind und Schaf. Dazu gehören u. a. der weniger differenzierte, dorsal unbefestigte Magen von geringer Kapazität und entsprechend geringer Kaudalausdehnung, die kleine Milz, die relativ große Leber sowie der voluminösere Darm, der stets audi bis zur linken Bauchwand reicht.Das Reh wird nach Vergleichen mit zahlreichen afrikanischen Wild-wiederkäuern aufgrund der bisherigen morphologischen und physiologischen Befunde als ein charakteristischer Vertreter des Wiederkäuer-Ernährungstyps der Konzentratselektierer klassifiziert, der sich wesentlich vom Grasfresser-Typ unterscheidet.Auf praktische Anwendungsmoglichkeiten der topographisch-anatomi-schen Befunde in der Veterinarmedizin wird hingewiesen.〈section xml:id="abs1-2"〉〈title type="main"〉SummaryThe topographic and functional anatomy of the abdominal viscera of the roe (Capreolus capreolus L.)The external morphology, the topography and x-ray anatomy of the abdominal viscera and their functional changes were investigated in ten roes which had been formalinized in a lying or in a natural, standing position.In general, the structural principles are similar to those in other ruminant species but are distinguished clearly from the grass-eating domestic ruminants cattle and sheep by specific signs relating to feeding type. They include a less differentiated and dorsally unattached stomach with a small capacity and lesser caudal expansion; a small spleen and a relatively large liver and a more voluminous intestine which is extending always also to the left abdominal wall.In comparison with numerous African game ruminants and based on morphological findings and the physiological data so far available, the roe is classified as a characteristic representative of the ruminant feeding-type of ‘concentrate selector’ which is well-distinguished from the grass-eating type. The results of the topographic-anatomical investigations are discussed in view of their practical application in veterinary medicine.〈section xml:id="abs1-3"〉〈title type="main"〉RésuméL'anatomie topographique et fonctionelle des visceres abdominaux du Chevreuil (Capreolus capreolus L.)La morphologie externe, la topographie et l'anatomie radiologique des viscères abdominaux, ainsi que leurs modifications fonctionnelles, ont étéétudiées chez dix chevreuils fixés au formol en décubitus ou dans l'attitude dressée naturelle.Dans l'ensemble, les principes de l'organisation sont les mêmes que ceux des autres Ruminants, mais ils présentent des différences caractéristiques comparativement aux Bovins et maux Moutons domestiques, différences relatives a leur type d'alimentation. En particulier, l'estomac est moins différencié, dé-pourvu de fixation dorsale, moins étendu caudalement et d'une moindre capacité. La rate est petite, le foie relativement gros et l'intestin plus volumineux, au point d'entrer aussi en rapport avec la paroi abdominale gauche. Comparativement à une large série de Ruminants sauvages africains et sur la base des observations morphologiques et physiologiques actuellement disponibles, le Chevreuil est considéré comme un representant caractéristique des Ruminants à alimentation de type «concentre selectif», bien différent du type-«consommateur d'herbe». Les résultats de ces recherches d'Anatomie topographique sont discutés en vue de leur application pratique à la médecine vétérinaire.〈section xml:id="abs1-4"〉〈title type="main"〉ResumenSobre la anatomía topográfica y funcional de las visceras abdominales del cervato (Capredus capreolus L.)En 10 cervatos (fijados con formol en posicion parada o acostada) se examinó la morfología externa y la topografía, incluyendo la anatomia radiográfica, de los órganos abdominales y su estado funcional. Existe el plan general de la constitucion de los demás rumiantes, aunque diferenciándose claramente de los rumiantes domésticos (ganado vacuno y ovejas) en lo que se refiere a características específicas del grupo, entre las cuales pueden citarse: el estómago poco diferenciado, que no está fijado en la parte dorsal y tiene una capacidad reducida así como muy poca extensión caudal; igualmente se encuentra un bazo pequeño, un hígado relativamente grande y un intestino voluminoso, que se extiende hasta el lado izquierdo de la pared abdominal.Luego de compararlo con varios rumiantes del Africa y debido a los hallazgos morfológicos y fisiológicos arriba mencionados, el cervato puede clasificarse como representante tipico de los rumiantes que utilizan alimentos concentrados, destacándose claramente de los comen grama. Además, se señala la aplicación práctica de los hallazgos antómicos y topográficos para la Me-dicina Veterinaria en general.

Notizen: [Auszug] Many galaxies are thought to have supermassive black holes at their centres—more than a million times the mass of the Sun. Measurements of stellar velocities and the discovery of variable X-ray emission have provided strong evidence in favour of such a black hole at the centre of the ...