8,046 research outputs found
EXOTIC AQUATIC PLANTS-SOME GOOD; SOME BAD
Aquatic plants, like all other plants, may be weeds in one location and a source of income and therefore coveted in another location. Introduction of exotic aquatic plants to the United States has always proceeded at a rapid rate. Many plants were brought in for horticultural or agricultural purposes. A greater number of aquatic species were brought in as aquarium plants and then accidentally or purposely introduced into the wild as a future source of income. A much lesser number have been introduced into natural waters from ballast pumpage. Most are of tropical or semi-tropical origin and initially were confined to waters in Hawaii, Florida, or California. Expansion of their range to other states has progressed until many exotic aquatic plants have become both a problem to water managers and a source of profit to the aquarium industry. As a rule exotic plants are not considered pests unless they are highly invasive. It is generally recognized that the nonindigenous aquatic plant species which are most invasive include hydrilla (Hydrilla verticillata), Eurasian watermilfoil (Myriophyllum spicatum), waterlettuce (Pistia stratiotes), alligatorweed (Alternanthera philoxeroides), parrot-feather (Myriophyllum aquaticum), egeria (Egeria densa), and waterhyacinth (Eichhornia crassipes). The latter is recognized as the world\u27s worst aquatic weed and in many areas the most prolific. Very few aquatic plant species are reported to have been accidentally introduced. These are usually from ship\u27s ballast and include waterlettuce, alligatorweed, and salvinia (Salvinia minima). Horticulturists are credited with the introduction of the waterhyacinth for its showy flowers. Hydrilla, egeria, parrotfeather, Eurasian watermilfoil, limnophila (Limnophila sessiflora), and hygrophila (Hygrophila polysperma) were all introduced by the aquarium trade and often sold as oxygenators. In areas where water conditions are favorable and the native vegetation is disturbed, these invasive species rapidly become the dominant species
Two New Heuristics in Response to Formulaic Writing: What Lies beyond Oversimplified Composition Instruction
Many high school and college composition students have misused formulaic organizational structures, most conspicuously the five-paragraph theme, as invention tools. This misappropriation comes from teacher and student tendencies to oversimplify both the processes of writing instruction and its practice into countable and inflexible forms. In order to help students move towards improved invention models that respond to the overall rhetorical situation, this dissertation offers two new models of invention, the x, y thesis and the argument guide models. Beginning at the invention stage and extending recursively to all stages of the writing process, these two heuristics help guide students towards informed and analytical choices that respectively build relationships between parts and encourage asymmetrical, content-driven extensions of ideas. These models, individually and collectively, assist students in their efforts to restore a balance between content and form because the models set the students’ invented content at the core of a nonlinear rhetorical action – the composition of an essay that involves all phases of process writing
Type Ia supernova diversity: Standardizing the candles
Future use of type Ia supernovae for cosmology aims not only to determine the
equation of state of dark energy, but also to constrain possible variations in
its value. To achieve this goal, supernovae need to become better calibrated
standard candles - not only to improve the precision of the measurement, but
more importantly to gain better control over systematic uncertainties in order
to ensure the accuracy of the result.
Here we report on a project to quantify the diversity in type Ia supernovae,
and to look for trends and/or sub-types that can be used to improve their
calibration as standard candles. We implement a version of principal component
analysis on type Ia supernova spectra. Although the quantity of data is not
sufficient to draw any firm conclusions we show that this method holds promise
for, at the very least, effectively separating peculiar supernovae. Whether it
can be further used to improve the calibration of normal type Ia's remains a
project for future study.Comment: Conference Proceedings. Cefalu 2006, The multicoloured landscape of
compact objects and their explosive origins. Six pages, three figure
Open/Closed String Topology and Moduli Space Actions via Open/Closed Hochschild Actions
In this paper we extend our correlation functions to the open/closed case.
This gives rise to actions of an open/closed version of the Sullivan PROP as
well as an action of the relevant moduli space. There are several unexpected
structures and conditions that arise in this extension which are forced upon us
by considering the open sector. For string topology type operations, one cannot
just consider graphs, but has to take punctures into account and one has to
restrict the underlying Frobenius algebras. In the moduli space, one first has
to pass to a smaller moduli space which is closed under open/closed duality and
then consider covers in order to account for the punctures
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