1,592 research outputs found
Evaluating the success of seed sowing in a New England grassland
Grassland habitat is declining in the northeastern United States, leading to a decline in associated native species. Consequently, there is considerable interest by land managers in conserving and restoring grassland habitats in the Northeast. However, unlike the Great Plains and Europe, quantitative monitoring of restoration sites is uncommon, making it difficult to improve new restoration projects. Here we evaluate a grassland restoration in Waterford, Connecticut to determine if mechanical clearing of woody vegetation combined with sowing 23 native grasses and forbs led to successful establishment of these species. We also compared cover, diversity, and colonization by exotic and woody species in planted and unplanted areas over time. In the third and fifth growing seasons after planting in 2006, we sampled the vegetation in the planted site, an unplanted zone within the planted grassland, and an adjacent unplanted grassland. Twenty of the 23 sown species established by 2010, and sown species dominated the planted area (70% of total cover). Despite the successful establishment of most sown species, species richness and diversity were no higher in the sown grassland than in adjacent unseeded areas. However, the sown grassland contained lower cover of non-native and invasive species. Big bluestem (Andropogon gerardii Vitman) established aggressively, potentially reducing both exotic colonization and native diversity. This study shows that sowing native grassland species can lead to the successful development of native-dominated grasslands. Results can inform future grassland restoration efforts in the Northeast and show that seeding with aggressive grass species may greatly impact restored plant communities
Transformative Education: The University Learning Community at UTK
Those who do not participate spontaneously are drawn out by others in the group. The discussion is intense, both emotionally and intellectually . . . The predominant tone is that of a group of good friends enjoying being with each other and relishing their mutual exploration of ideas. This is a typical Case Studies class in UTK\u27s University Learning Community
Formation and Collapse of Nonaxisymmetric Protostellar Cores in Planar Magnetic Interstellar Clouds: Formulation of the Problem and Linear Analysis
We formulate the problem of the formation and collapse of nonaxisymmetric
protostellar cores in weakly ionized, self-gravitating, magnetic molecular
clouds. In our formulation, molecular clouds are approximated as isothermal,
thin (but with finite thickness) sheets. We present the governing dynamical
equations for the multifluid system of neutral gas and ions, including
ambipolar diffusion, and also a self-consistent treatment of thermal pressure,
gravitational, and magnetic (pressure and tension) forces. The dimensionless
free parameters characterizing model clouds are discussed. The response of
cloud models to linear perturbations is also examined, with particular emphasis
on length and time scales for the growth of gravitational instability in
magnetically subcritical and supercritical clouds. We investigate their
dependence on a cloud's initial mass-to-magnetic-flux ratio (normalized to the
critical value for collapse), the dimensionless initial neutral-ion collision
time, and also the relative external pressure exerted on a model cloud. Among
our results, we find that nearly-critical model clouds have significantly
larger characteristic instability lengthscales than do more distinctly sub- or
supercritical models. Another result is that the effect of a greater external
pressure is to reduce the critical lengthscale for instability. Numerical
simulations showing the evolution of model clouds during the linear regime of
evolution are also presented, and compared to the results of the dispersion
analysis. They are found to be in agreement with the dispersion results, and
confirm the dependence of the characteristic length and time scales on
parameters such as the initial mass-to-flux ratio and relative external
pressure.Comment: 30 pages, 7 figures Accepted by Ap
2,2-Bis[(2-halo-4-aminophenoxy)phenyl]-hexafluoropropane
There are provided the aromatic diamines 2,2-bis-[(2-halo-4-aminophenoxy)-phenyl]hexafluoropropane, where the attached ortho halogen is preferably chlorine, and 4,4'-bis(4-aminophenoxy)biphenyl, as novel monomers for polyimide polymerizations. The former, when reacted with 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride, provides a polyimide having exceptional high-temperature performance. The latter diamine is a low-cost monomer for polyimide production
High-temperature polyimides prepared from 2,2-bis-[(2-halo-4-aminophenoxy)-phenyl]hexafluoropropane
There are provided the aromatic diamines 2,2-bis-[(2-halo-4-aminophenoxy)-phenyl]hexafluoropropane, where the attached ortho halogen is preferably chlorine, and 4,4'-bis(4-aminophenoxy)biphenyl, as novel monomers for polyimide polymerizations. The former, when reacted with 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride, provides a polyimide having exceptional high-temperature performance. The latter diamine is a low-cost monomer for polyimide production
Fiber reinforced thermoplastic resin matrix composites
Polyimide polymer composites having a combination of enhanced thermal and mechanical properties even when subjected to service temperatures as high as 700.degree. F. are described. They comprise (a) from 10 to 50 parts by weight of a thermoplastic polyimide resin prepared from 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane and (b) from 90 to 50 parts by weight of continuous reinforcing fibers, the total of (a) and (b) being 100 parts by weight. Composites based on polyimide resin formed from 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane and pyromellitic dianhydride and continuous carbon fibers retained at least about 50% of their room temperature shear strength after exposure to 700.degree. F. for a period of 16 hours in flowing air. Preferably, the thermoplastic polyimide resin is formed in situ in the composite material by thermal imidization of a corresponding amide-acid polymer prepared from 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane. It is also preferred to initially size the continuous reinforcing fibers with up to about one percent by weight of an amide-acid polymer prepared from 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane. In this way imidization at a suitable elevated temperature results in the in-situ formation of a substantially homogeneous thermoplastic matrix of the polyimide resin tightly and intimately bonded to the continuous fibers. The resultant composites tend to have optimum thermo-mechanical properties
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