19,946 research outputs found
Engineering models of the Martian atmosphere and surface
Mars surface and atmosphere models for landing module desig
Copper Complexation by Dissolved Organic Matter in arid Soils: A Voltametric Study
A voltammetric method was used to estimate the complexing capacity of water extracts from both desert soils sampled at the root zone of creosote and salt cedar plants, and in soils from interspace or background regions where no vegetative influence was apparent. The copper complexing capacity of water extracts of these desert soils was influenced by contact time and pH. In soils from the root zones of creosote and salt cedar plant, copper complexation capacities at pH 8 were from 5 µM to 60 µM after five min contact periods, while 18 h contact periods yielded copper complexation capacities of 40 µM–80 µM. Soils with no vegetative influence had copper complexing capacities of less the 2 µM. The copper complexing capacities of these soils are well correlated with the concentration of organic carbon in the water extract (r2 = 0.86). The abundance of soluble organic matter in the root zone of desert shrubs has the potential to control the solution speciation of Cu2+. The formation of soluble complexes should also have an important influence on the plant uptake and transport of copper, as well as other heavy metals in the root zones of desert shrubs and beyond
Seasonal Growth of Waterhyacinth in the Sacramento/San Joaquin Delta, California
Waterhyacinth (
Eichhornia crassipes
(Mart.) Solms), is a serious
problem in the Sacramento/San Joaquin Delta, California.
There is little published information on its phenology or
seasonal growth in this system. Waterhyacinths were sampled
at 2 to 3 week intervals from November, 1995 to July, 1997
and the following measurements were made on individual
plants: dry weight, height, number of living leaves, number of
dead leaves, and the width of the largest lamina. (PDF has 4 pages.
Feasibility of Interstellar Travel
The feasibility of interstellar flight is discussed. Mathematical equations for single-stage and multistage rocket propulsion are developed; velocity data and transit times are presented. The conclusions indicate that interstellar travel is theoretically feasible by utilizing known staged nuclear-energy systems
Do tissue carbon and nitrogen limit population growth of weevils introduced to control waterhyacinth at a site in the Sacramento-San Joaquin Delta, California?
Waterhyacinth (Eichhornia crassipes(Mart.) Solms), is a serious problem in the Sacramento Delta. Two weevil species
(Neochetina bruchi Hustache and N. eichhorniae
Warner) have been introduced as biological control agents. The purpose of this study was to test the hypothesis that nitrogen (N) in the tissue of waterhyacinth was not sufficient to support weevil growth and reproduction. Because it grows better on plants with high N content and because it has a greater impact on the growth of high N plants, N. bruchi may be a more effective biological control agent in the Sacramento Delta
Electronic strain-level counter
Counter for aircraft counts and records number of times the strain at a point in a structural member exceeds each of four preset levels. Counter uses 28 volt dc power supply, metallic resistance strain gage bridge as sensor, integrated and solid state circuits for signal processing, and electromechanical counters for data storage and readout
Interactions between American pondweed and monoecious hydrilla grown in mixtures
To assess the potential for monoecious hydrilla (
Hydrilla
verticillata
(L.f.) Royle) to invade existing aquatic plant communities,
monoecious hydrilla was grown in mixtures with
American pondweed (
Potamogeton nodosus
Poiret). When
grown with hydrilla
from axillary turions, American pondweed
was a stronger competitor. When grown with hydrilla
from tubers, American pondweed was equally as strong a
competitor as hydrilla
Seasonal Changes in Chemical Composition of Eurasion Watermilfoil (Myriophyllum spicatum L.) and Water Temperature at Two Sites in northern California: implications for Herbivory
We compared seasonal changes in Eurasian watermilfoil (Myriophyllum spicatum L.) characteristics and water temperature for a shallow poind in Davis, CA, and the Truckee River, near Tahoe City, CA. Tissue C and N were 15% lower in plants from the Truckee River than in plants from the Davis pond. Seasonal fluctuations in tissue N were also different. Mean phenolic acid content of Truckee River palnts (162yM g-1) was less than those from the shallow pond (195 yM g-1). Phenolic acid content was positively related to tissue C for Truckee River and Davis pond plants and, tissue C:N ratio for Truckee River plants. Mean monthly water temperature (1990 to 1998) for the Truckee River site was less than 20 C. Water temperatures were warmer in August and September at this site. However, Eurasian watermilfoil collected during these months was characterized by lower levels of tissue N. During a 29-month period beginning January 1994, mean monthly water temperature for the Davis pond exceeded 20 C, only during July to September 1995. Tissue N was generally greater during summer for watermilfoil growing in the pond. These results imply that Eurasian watermilfoil biological control agents may have different developmental rates in these habitats, and thus different impacts on watermilfoil populations
Impure Thoughts on Inelastic Dark Matter
The inelastic dark matter scenario was proposed to reconcile the DAMA annual
modulation with null results from other experiments. In this scenario, WIMPs
scatter into an excited state, split from the ground state by an energy delta
comparable to the available kinetic energy of a Galactic WIMP. We note that for
large splittings delta, the dominant scattering at DAMA can occur off of
thallium nuclei, with A~205, which are present as a dopant at the 10^-3 level
in NaI(Tl) crystals. For a WIMP mass m~100GeV and delta~200keV, we find a
region in delta-m-parameter space which is consistent with all experiments.
These parameters in particular can be probed in experiments with thallium in
their targets, such as KIMS, but are inaccessible to lighter target
experiments. Depending on the tail of the WIMP velocity distribution, a highly
modulated signal may or may not appear at CRESST-II.Comment: 3 pages, 1 figure, accepted for publication in Physical Review
Letter
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