199 research outputs found
Fluctuations and Relationships of Selected Physiochemical Parameters in Dardanelle Reservoir, Arkansas, 1975-1982
Annual and seasonal fluctuations and relationships are described for discharge, turbidity, chloride, total hardness, conductivity and suspended solids over an eight-year period in Dardanelle Reservoir. The parameters fluctuated rather widely primarily in response to seasonal patterns of rainfall. Chloride and conductivity were related and generally fluctuated together as did turbidity and suspended solids. Hardness appeared to vary independently of the others prior to 1979 then varied more closely with chloride after March 1979. Inherent differences between the Illinois Bayou arm and the main Arkansas River sections complicated the precise identification of any overall impact of power plant operation. No significant long term changes were seen, but chloride declined gradually whereas hardness and conductivity increased slightly. Suspended solids exhibited a significant rise in 1982
Dragonflies of (Anisoptera) Arkansas
Previous publications have recorded 69 species of dragonflies for Arkansas. Three of these are deleted, but state records for 21 new species are reported herein, bringing the list to 87 species. Based on lists from adjacent states, an additional nine species are listed as probably occurring in Arkansas. County records are given for both naiads and adults of each species, as well as first and last capture dates for adults. Specific location and capture date are given for new state records when such data are available. The most species (39) have been reported from Washington County. Twenty-nine counties list from 1-5 species, and six counties list no records
Phytoplankton Community Structure in Dardanelle Reservoir, Arkansas, 1975-1982
Phytoplankton data were collected with standard equipment and procedures over an eight-year period (1975-1982) in Dardanelle Reservoir, Arkansas. Community abundance and diversity at the genus level are described. Sixty-five genera representing 35 families and five divisions were identified. Total phytoplankton abundance and diversity were quite uniform among the stations but fluctuated considerably with time. These fluctuations did not correspond clearly with season. Dominant taxa were seasonal, though, with diatoms being usually dominant in January, April and October, and blue-greens dominant in July. The phytoplankton community structure has not been significantly altered by the operation of ANO Unit I
Phytoplankton Community Abundance and Diversity in Dardanelle Reservoir, Arkansas, 1981-1990
Phytoplankton samples were collected quarterly from 1981-1990 at five stations representing discharge water from Arkansas Nuclear One, a nuclear generating station, and four control or dispersal evaluation stations. Seventy-five taxa representing five divisions were identified and enumerated. Community structure was evaluated using abundances, number of taxa, and Margalef\u27s Richness, Shannon\u27s Heterogeneity and Pielou\u27s Evenness indices. No long-term trends were identified, but the beginning of cyclic variations, with a 7-year periodicity, in abundance, number of taxa, and Shannon\u27s and Pielou\u27s indices were apparent. Margalef\u27s index values were constant during most of the study period. For all samples, t-tests and Mann-Whitney U tests between station 5 (discharge) and each of four control stations, revealed no significant differences with any variable
First Record of Leptodora kindti in Dardanelle Reservoir and Status of Other Recent Additions to Dardanelle Fauna
Long-Term Study of Benthos in Dardanelle Reservoir
Winter, spring, summer, and autumn samples were collected with a 15.24x15.24-cm Ekman grab from five stations on Dardanelle Reservoir, Pope County, Arkansas during the 24-year period from 1970-1993. Twenty-three taxa representing the eight phyla, Cnidaria, Nematoda, Nematomorpha, Entoprocta, Ectoprocta, Mollusca, Annelida, and Arthropoda, were collected. Numerically, oligochaetes comprised 36%, whereas chironomid larvae, Chaoborus larvae, and Hexagenia naiads mad up 29.7, 17, and 12%, respectively, of the samples. Asiatic clams, fingernail clams, amphipods, and Urnatella were collected frequently during the last 10 years but were not abundant. Other taxa were taken infrequently but consistently during the study period. Densities of all taxa fluctuated widely but generally not in close association with season, station, or year. A few significant differences (t-tests; cx=0.05) occurred between stations 5 (discharge) vs. 16 (intake) and 5 vs. 21 (upstream control), but most of them were due to natural differences in substrate composition. Margalef s Richness and Shannon\u27s Heterogeneity Indices did not identify any time-based trends and, with one exception, did not indicate any significant differences between stations
Interstellar Scintillation Observations of 146 Extragalactic Radio Sources
From 1979--1996 the Green Bank Interferometer was used by the Naval Research
Laboratory to monitor the flux density from 146 compact radio sources at
frequencies near 2 and 8 GHz. We filter the ``light curves'' to separate
intrinsic variations on times of a year or more from more rapid interstellar
scintilation (ISS) on times of 5--50 d. Whereas the intrinsic variation at 2
GHz is similar to that at 8 GHz (though diminished in amplitude), the ISS
variation is much stronger at 2 than at 8 GHz. We characterize the ISS
variation by an rms amplitude and a timescale and examine the statistics of
these parameters for the 121 sources with significant ISS at 2 GHz. We model
the scintillations using the NE2001 Galactic electron model assuming the
sources are brightness-limited.
We find the observed rms amplitude to be in general agreement with the model,
provided that the compact components of the sources have about 50% of their
flux density in a component with maximum brightness temperatures
--K. Thus our results are consistent with cm-wavelength VLBI
studies of compact AGNs, in that the maximum brightness temperatures found are
consistent with the inverse synchrotron limit at K, boosted
in jet configurations by Doppler factors up to about 20. The average of the
observed 2 GHz ISS timescales is in reasonable agreement with the model at
Galactic latitudes above about 10\de. At lower latitudes the observed
timescales are too fast, suggesting that the transverse plasma velocity
increases more than expected beyond about 1 kpc.Comment: 32 pages, 16 figures. Submitted to Ap
Zooplankton Community Structure in Dardanelle Reservoir, Arkansas, 1975-1982
Zooplankton was collected at 10 stations in Dardanelle Reservoir from 1975 to 1982. Current data were compared to a five-year preoperational study phase. Rotifer taxa strongly dominated the community. Overall abundance was higher, variety about the same and diversity lower than those of comparable studies. Thermal discharges caused a dominance shift between two rotifer taxa, slightly depressed abundance and variety, did not noticeably affect diversity and elevated the phytoplankton/zooplankton ratio. Heated effluent also stimulated stronger fluctuations in abundance and variety. Other studies indicate that in upper sections of the Arkansas River drainage, microcrustaceans dominate lake habitats whereas rotifers dominate river habitats. In similar northern and eastern habitats, microcrustaceans were generally dominant
The stationary phase point method for transitional scattering: diffractive radio scintillation for pulsar
The stationary phase point (SPP) method in one-dimensional case is introduced
to treat the diffractive scintillation. From weak scattering, where the SPP
number N=1, to strong scattering (N1), via transitional scattering regime
(N2,3), we find that the modulation index of intensity experiences the
monotonically increasing from 0 to 1 with the scattering strength,
characterized by the ratio of Fresnel scale \rf to diffractive scale
\rdiff.Comment: Hanas Meeting paper, appear in ChJAA, 2006, 6, Su
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