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Morphological Classes (morphological + class)
Selected AbstractsAcquisition of Spanish Gender Agreement in Two Learning Contexts: Study Abroad and At HomeFOREIGN LANGUAGE ANNALS, Issue 2 2010Christina Isabelli-García Abstract: The goal of this study is to describe the acquisition rate for gender acquisition in Spanish and to show whether individual variability and language contact may affect this rate. The participants were intermediate second language Spanish (first language English) learners in the study abroad and at-home contexts over a 4-month period. The participants received grammaticality judgment tests coded for morphological class of the modified noun as well as attributive and predicative adjectives. Data were also collected on social behavior and language contact in Spanish and English in order to explain data outcome. The findings suggest that no difference exists between the two learning contexts and that social behavior and language contact abroad have minimal influence on acquisition rate. [source] Star formation in close pairs selected from the Sloan Digital Sky SurveyMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2004B. Nikolic ABSTRACT The effect of galaxy interactions on star formation has been investigated using Data Release One of the Sloan Digital Sky Survey (SDSS). Both the imaging and spectroscopy data products have been used to construct a catalogue of nearest companions to a volume-limited (0.03 < z < 0.1) sample of galaxies drawn from the main galaxy sample of SDSS. Of the 13 973 galaxies in the volume-limited sample, we have identified 12 492 systems with companions at projected separations less than 300 kpc. Star formation rates for the volume-limited sample have been calculated from extinction and aperture corrected H, luminosities and, where available, IRAS data. Specific star formation rates were calculated by estimating galaxy masses from z -band luminosities, and r -band concentration indices were used as an indicator of morphological class. The mean specific star formation rate is significantly enhanced for projected separations less than 30 kpc. For late-type galaxies, the correlation extends out to projected separations of 300 kpc and is most pronounced in actively star-forming systems. The specific star formation rate is observed to decrease with increasing recessional velocity difference, but the magnitude of this effect is small compared to that associated with the projected separation. We also observe a tight relationship between the concentration index and pair separation; the mean concentration index is largest for pairs with separations of approximately 75 kpc and declines rapidly for separations smaller than this. This is interpreted as being due to the presence of tidally triggered nuclear starbursts in close pairs. Further, we find no dependence of star formation enhancement on the morphological type or mass of the companion galaxy. [source] The musculotendinous system of an anguilliform swimmer: Muscles, myosepta, dermis, and their interconnections in Anguilla rostrataJOURNAL OF MORPHOLOGY, Issue 1 2008Nicole Danos Abstract Eel locomotion is considered typical of the anguilliform swimming mode of elongate fishes and has received substantial attention from various perspectives such as swimming kinematics, hydrodynamics, muscle physiology, and computational modeling. In contrast to the extensive knowledge of swimming mechanics, there is limited knowledge of the internal body morphology, including the body components that contribute to this function. In this study, we conduct a morphological analysis of the collagenous connective tissue system, i.e., the myosepta and skin, and of the red muscle fibers that sustain steady swimming, focusing on the interconnections between these systems, such as the muscle-tendon and myosepta-skin connections. Our aim is twofold: (1) to identify the morphological features that distinguish this anguilliform swimmer from subcarangiform and carangiform swimmers, and (2) to reveal possible pathways of muscular force transmission by the connective tissue in eels. To detect gradual morphological changes along the trunk we investigated anterior (0.4L), midbody (0.6L), and posterior body positions (0.75L) using microdissections, histology, and three-dimensional reconstructions. We find that eel myosepta have a mediolaterally oriented tendon in each the epaxial and hypaxial regions (epineural or epipleural tendon) and two longitudinally oriented tendons (myorhabdoid and lateral). The latter two are relatively short (4.5,5% of body length) and remain uniform along a rostrocaudal gradient. The skin and its connections were additionally analyzed using scanning electron microscopy (SEM). The stratum compactum of the dermis consists of ,30 layers of highly ordered collagen fibers of alternating caudodorsal and caudoventral direction, with fiber angles of 60.51 ± 7.05° (n = 30) and 57.58 ± 6.92° (n = 30), respectively. Myosepta insert into the collagenous dermis via fiber bundles that pass through the loose connective tissue of the stratum spongiosum of the dermis and either weave into the layers of the stratum compactum (weaving fiber bundles) or traverse the stratum compactum (transverse fiber bundles). These fiber bundles are evenly distributed along the insertion line of the myoseptum. Red muscles insert into lateral and myorhabdoid myoseptal tendons but not into the horizontal septum or dermis. Thus, red muscle forces might be distributed along these tendons but will only be delivered indirectly into the dermis and horizontal septum. The myosepta-dermis connections, however, appear to be too slack for efficient force transmission and collagenous connections between the myosepta and the horizontal septum are at obtuse angles, a morphology that appears inadequate for efficient force transmission. Though the main modes of undulatory locomotion (anguilliform, subcarangiform, and carangiform) have recently been shown to be very similar with respect to their midline kinematics, we are able to distinguish two morphological classes with respect to the shape and tendon architecture of myosepta. Eels are similar to subcarangiform swimmers (e.g., trout) but are substantially different from carangiform swimmers (e.g., mackerel). This information, in addition to data from kinematic and hydrodynamic studies of swimming, shows that features other than midline kinematics (e.g., wake patterns, muscle activation patterns, and morphology) might be better for describing the different swimming modes of fishes. J. Morphol., 2008. © 2007 Wiley-Liss, Inc. [source] Statistical morphological analysis of hippocampal principal neurons indicates cell-specific repulsion of dendrites from their own cellJOURNAL OF NEUROSCIENCE RESEARCH, Issue 2 2003Alexei V. Samsonovich Abstract Traditionally, the sources of guidance cues for dendritic outgrowth are mainly associated with external bodies (A) rather than with the same neuron from which dendrites originate (B). To quantify the relationship between factors A and B as determinants of the adult dendritic shape, the morphology of 83 intracellularly characterized, stained, completely reconstructed, and digitized principal neurons of the rat hippocampus was statistically analyzed using Bayesian optimization. It was found that the dominant directional preference (tropism) manifested in dendritic turns is to grow away from the soma rather than toward the incoming fibers or in any other fixed direction; therefore, B is predominant. Results are robust and consistent for all examined morphological classes (dentate gyrus granule cells, basal and apical trees of CA3 and CA1 pyramidal cells). In addition, computer remodeling of neurons based on the measured parameters produced virtual structures consistent with real morphologies, as confirmed by measurement of several global emergent parameters. Thus, the simple description of dendritic shape based on dendrites' tendency to grow straight, away from their own soma, and with additional random deflections, proves remarkably accurate and complete. Although based on adult neurons, these results suggest that dendritic guidance during development may be associated primarily with the host cell. This possibility challenges the traditional concept of dendritic guidance: in that hippocampal cells are densely packed and have highly overlapping dendritic fields, the somatodendritic repulsion must be cell specific. Plausible mechanisms involving extracellular effects of spikes are discussed, together with feasible experimental tests and predicted results. © 2002 Wiley-Liss, Inc. [source] Flat galaxies in the SDSS DR6ASTRONOMISCHE NACHRICHTEN, Issue 9-10 2009S.J. Kautsch Abstract This study presents the fractions of different spiral galaxy types from a complete and homogeneous sample of 15 127 edge-on disk galaxies extracted from the sixth data release from the Sloan Digital Sky Survey. The sample is divided in broad morphological classes and sub types consisting of galaxies with bulges, intermediate types and galaxies which appear bulgeless. A small fraction of disky irregulars is also detected. The morphological separation is based on automated classification criteria which resemble the bulge sizes and the flatness of the disks. Each of these broad classes contains about 1/3 of the total sample. Using strict criteria for selecting pure bulgeless galaxies leads to a fraction of 15 % of simple disk galaxies (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Radio source populations: Results from SDSSASTRONOMISCHE NACHRICHTEN, Issue 2-3 2009P.N. Best Abstract This contribution provides a review of our current understanding of radio source populations and their host galaxies, as derived from studies of the local Universe, in particular using the Sloan Digital Sky Survey. Evidence is presented that low luminosity radio sources are fundamentally distinct objects to high radio luminosity sources and optically or X-ray selected AGN, suggesting that these are fuelled by a different mechanism. The low-luminosity radio sources are argued to be fuelled by the accretion of hot gas from their surrounding X-ray haloes, and this offers a potential feedback loop via which the radio-loud AGN can control the cooling of the hot gas, and thus the growth of their host galaxy. The energetic output of the radio sources is derived in order to show that this is indeed feasible. It is emphasised that the difference between these two modes of AGN fuelling is distinct from that of the two different radio morphological classes of radioloud AGN (Fanaroff-Riley classes 1 and 2). The origin of the FR-dichotomy is investigated using Sloan data, and argued to be associated with the environment and evolution of the radio sources. Finally, the role of CSS and GPS sources within this picture is discussed (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Edge-on disk galaxies in the SDSS DR6: Fractions of bulgeless and other disk galaxiesASTRONOMISCHE NACHRICHTEN, Issue 1 2009S.J. KautschArticle first published online: 2 JAN 200 Abstract The aim of this study is to determine the fractions of different spiral galaxy types, especially bulgeless disks, from a complete and homogeneous sample of 15 127 edge-on disk galaxies extracted from the sixth data release from the Sloan Digital Sky Survey. The sample is divided in broad morphological classes and sub types consisting of galaxies with bulges, intermediate types and galaxies which appear bulgeless. A small fraction of disky irregulars is also detected. The morphological separation is based on automated classification criteria which resemble the bulge sizes and the flatness of the disks. Each of these broad classes contains about 1/3 of the total sample. Using strict criteria for selecting pure bulgeless galaxies leads to a fraction of 15% of simple disk galaxies. We compare this fraction to other galaxy catalogs and find an excellent agreement of the observed frequency of bulgeless galaxies. Although the fraction of simple disk galaxies in this study does not represent a "cosmic" fraction of bulgeless galaxies, it shows that the relative abundance of pure disks is comparable to other studies and offers a profound value of the frequency of simple disks in the local Universe. This fraction of simple disks emphasizes the challenge for formation and evolution models of disk galaxies since these models are hard pressed to explain the observed frequency of these objects (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | |||||||||||||