Ultrastructural Observations on the Septal Pore in Cronartium Flaccidum (Alb. Et Schw.) Wint. Also in Relation to the Taxonomy of the Uredinales

SUMMARYThe fine structure of the septum and pore in the monokaryotic and dikaryotic vegetative mycelium of Cronartium flaccidum was studied. Some ultrastructural observations on the hyphal cell of this fungus were also carried out. The hyphal septa become progressively thinner towards the pore; the septal pore shows none of the swellings and of the structures resembling the parenthesome which characterize the dolipore septum of higher Basidiomycetes. The septal pore of C. flaccidum as it as been seen in other Uredinales investigated up now, is a very simple structure morphologically similar to the septal pore of Ascomycetes. Some formations which make up the septal pore apparatus that is amorphous and electron-dense material, differentiated organelle-free cytoplasm and microbodies were observed near the septum and pore in both nuclear phases of the mycelium. It is accepted a relationship between the occurrence of microbodies and the occurrence and function of the dense material at the pore region likely t..

Neural Nets and Star/Galaxy Separation in Wide Field Astronomical Images

One of the most relevant problems in the extraction of scientifically useful information from wide field astronomical images (both photographic plates and CCD frames) is the recognition of the objects against a noisy background and their classification in unresolved (star-like) and resolved (galaxies) sources. In this paper we present a neural network based method capable to perform both tasks and discuss in detail the performance of object detection in a representative celestial field. The performance of our method is compared to that of other methodologies often used within the astronomical community.Comment: 6 pages, to appear in the proceedings of IJCNN 99, IEEE Press, 199

Why do Large Animals Never Actuate Their Jumps with Latch-Mediated Springs? Because They can Jump Higher Without Them.

As animals get smaller, their ability to generate usable work from muscle contraction is decreased by the muscle's force-velocity properties, thereby reducing their effective jump height. Very small animals use a spring-actuated system, which prevents velocity effects from reducing available energy. Since force-velocity properties reduce the usable work in even larger animals, why don't larger animals use spring-actuated jumping systems as well? We will show that muscle length-tension properties limit spring-actuated systems to generating a maximum one-third of the possible work that a muscle could produce-greatly restricting the jumping height of spring-actuated jumpers. Thus a spring-actuated jumping animal has a jumping height that is one-third of the maximum possible jump height achievable were 100% of the possible muscle work available. Larger animals, which could theoretically use all of the available muscle energy, have a maximum jumping height that asymptotically approaches a value that is about three times higher than that of spring-actuated jumpers. Furthermore, a size related "crossover point" is evident for these two jumping mechanisms: animals smaller than this point can jump higher with a spring-actuated mechanism, while animals larger than this point can jump higher with a muscle-actuated mechanism. We demonstrate how this limit on energy storage is a consequence of the interaction between length-tension properties of muscles and spring stiffness. We indicate where this crossover point occurs based on modeling and then use jumping data from the literature to validate that larger jumping animals generate greater jump heights with muscle-actuated systems than spring-actuated systems

A New Approach to the Study of Stellar Populations in Early-Type Galaxies: K-band Spectral Indices and an Application to the Fornax Cluster

New measurements of K-band spectral features are presented for eleven early-type galaxies in the nearby Fornax galaxy cluster. Based on these measurements, the following conclusions have been reached: (1) in galaxies with no signatures of a young stellar component, the K-band Na I index is highly correlated with both the optical metallicity indicator [MgFe]' and central velocity dispersion; (2) in the same galaxies, the K-band Fe features saturate in galaxies with sigma > 150 km/s while Na I (and [MgFe]') continues to increase; (3) [Si/Fe] (and possibly [Na/Fe]) is larger in all observed Fornax galaxies than in Galactic open clusters with near-solar metallicity; (4) in various near-IR diagnostic diagrams, galaxies with signatures of a young stellar component (strong Hbeta, weak [MgFe]') are clearly separated from galaxies with purely old stellar populations; furthermore, this separation is consistent with the presence of an increased number of M-giant stars (most likely to be thermally pulsating AGB stars); (5) the near-IR diagrams discussed here seem as efficient for detecting putatively young stellar components in early-type galaxies as the more commonly used age/metallicity diagnostic plots using optical indices (e.g Hbeta vs. [MgFe]').Comment: 47 pages, 16 figures, ApJ accepte