1,682 research outputs found

    On the cohomology of stable map spaces

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    We describe an approach to calculating the cohomology rings of stable map spaces. The method we use is due to Akildiz-Carrell and employs a C^*-action and a vector field which is equivariant with respect to this C^*-action. We give an explicit description of the big Bialynicky-Birula cell of the C^*-action on Mbar_00(P^n,d) as a vector bundle on Mbar_0d. This is used to calculate explicitly the cohomology ring of Mbar_00(P^n,d) in the cases d=2 and d=3. Of particular interest is the case as n approaches infinity.Comment: 63 page

    Annual Survey Of Antitrust Developments 1977-1978

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    Ozone Induces Nerve Growth Factor Release from Rat Tracheal Epithelial Cells during an Early Postnatal Critical Period

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    Ozone, one of the major air pollutants in urban areas, produces epithelial cell injury and inflammation in the airways upon exposure. Previous studies have shown that ozone exposure leads to increased substance P (SP) expression in nerves innervating the smooth muscle in the extrapulmonary airway. Nerve growth factor (NGF), a neurotrophin, is known to increase SP expression. To determine the effect of ozone exposure on the release of NGF, a cell culture technique was developed for studying a homogenous rat tracheal epithelial cell population for analysis of NGF mRNA and protein expression. Furthermore, to determine if this effect is age-dependent, a critical period exposure paradigm was used. Rat pups exposed to ozone at postnatal day (PD) 6 showed an increase in the level of NGF mRNA while pups exposed after PD 6 showed no change in NGF expression. When rat pups exposed to ozone on PD 6 were reexposed at a later date, an increase in NGF mRNA was observed. These data suggest that exposure to ozone has an effect on NGF expression in early postnatal life and that this exposure might play a role in ozone sensitivity later in life

    Bacterial endophyte communities in the foliage of coast redwood and giant sequoia

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    The endophytic bacterial microbiome, with an emerging role in plant nutrient acquisition and stress tolerance, is much less studied in natural plant populations than in agricultural crops. In a previous study, we found consistent associations between trees in the pine family and acetic acid bacteria (AAB) occurring at high relative abundance inside their needles. Our objective here was to determine if that pattern may be general to conifers, or alternatively, is more likely restricted to pines, or conifers growing in nutrient limited and exposed environments. We used 16S rRNA pyrosequencing to characterize the foliar endophyte communities of two conifers in the Cupressaceae family: Two coast redwood (Sequoia sempervirens) populations and one giant sequoia (Sequoiadendron giganteum) population were sampled. Similar to the pines, the endophyte communities of the giant trees were dominated by Proteobacteria, Firmicutes, Acidobacteria, and Actinobacteria. However, although some major OTUs occurred at a high relative abundance of 10-40% in multiple samples, no specific group of bacteria dominated the endophyte community to the extent previously observed in high-elevation pines. Several of the dominating bacterial groups in the coast redwood and giant sequoia foliage (e.g. Bacillus, Burkholderia, Actinomycetes) are known for disease- and pest suppression, raising the possibility that the endophytic microbiome protects the giant trees against biotic stress. Many of the most common and abundant OTUs in our dataset were most similar to 16S rRNA sequences from bacteria isolated from lichens or arctic plants. For example, an OTU belonging to the uncultured Rhizobiales LAR1 lineage, which is commonly associated with lichens, was observed at high relative abundance in many of the coast redwood samples. The taxa shared between the giant trees, arctic plants, and lichens may be part of a broadly defined endophyte microbiome common to temperate, boreal, and tundra ecosystems

    A Study in the Ring Structure of Methylated Sugars

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    The report will show that methylation of glucose with methyl sulphate and sodium hydroxide, if carried out at lower temperatures and in less alkaline solutions than usually employed, yields methylated gamma glucoside. The value of (1) the rate of oxidation by potassium permanganate and (2) the acid concentration required for hydrolysis, as tests for gamma glucosides, will also be discussed

    Attribute Diversity Determines the Systematicity Gap in VQA

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    The degree to which neural networks can generalize to new combinations of familiar concepts, and the conditions under which they are able to do so, has long been an open question. In this work, we study the systematicity gap in visual question answering: the performance difference between reasoning on previously seen and unseen combinations of object attributes. To test, we introduce a novel diagnostic dataset, CLEVR-HOPE. We find that while increased quantity of training data does not reduce the systematicity gap, increased training data diversity of the attributes in the unseen combination does. In all, our experiments suggest that the more distinct attribute type combinations are seen during training, the more systematic we can expect the resulting model to be.Comment: 18 pages, 20 figure

    Numerical Simulation of a possible origin of the positive radial metallicity gradient of the thick disk

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    We analyze the radial and vertical metallicity and [alpha/Fe] gradients of the disk stars of a disk galaxy simulated in a fully cosmological setting with the chemodynamical galaxy evolution code, GCD+. We study how the radial abundance gradients vary as a function of height above the plane and find that the metallicity ([alpha/Fe]) gradient becomes more positive (negative) with increasing height, changing sign around 1.5 kpc above the plane. At the largest vertical height (2 2 kpc at the outer region, because of the lower gravitational restoring force of the disk, i.e. flaring. As a result, the fraction of younger stars with higher metallicity due to the age-metallicity relation becomes higher at the outer radii, which makes the median metallicity higher at the outer radii. Combining this result with the recently observed age-metallicity and age-velocity dispersion relation for the Milky Way thick disk stars suggested by Haywood et al. (2013), we argue that the observed (small) positive radial metallicity gradient at large heights of the Milky Way disk stars can be explained by the flaring of the younger thick and/or thin disk stars
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