186 research outputs found
Life Cycle of \u3ci\u3eIsoperla Lata\u3c/i\u3e (Plecoptera: Perlodidae) in a Central Wisconsin Trout Stream
Monthly qualitative samples of Isoperla lata Frison were made from January 1992 to June 1993 in Ripley Creek, a small second order trout stream in Lincoln County Wisconsin. Additional collecting and an in-stream hatching experiment were conducted in 1994. This species exhibited an S1 (slow) univoltine life cycle. Emergence was synchronous and occurred in late April through early May when stream temperatures in the field were approximately 9-14° C and laboratory stream temperatures were 7-17° C. Laboratory longevity was 2-25 (x = 18.2 ± 4.51) days for males and 7-39 (x = 21.7 ± 5.35) days for females. Mean fecundity of dissected females was 322 ± 122 eggs/female. Females did not deposit egg masses in the laboratory until being held together with males inside modified screened plastic containers. Field-collected females did not have eggs. The egg shape was ovoid and circular in cross section. Mature eggs were light brown and measured 371.7 ± 12.6 mm and 260.7 ± 10.2 mm in length and width respectively. Eggs required a 40-46 day in-stream incubation period and first instar nymphs hatched syn- chronously over a two day period when stream temperature reached 20°C. Nymphal growth was nearly exponential from June to January and then declined until emergence. The greatest growth increment occurred between June and October and the average maximum size attained occurred in February. Males and females had approximately 18 and 19 instars respectively. Nymphs were primarily carnivorous throughout development and fed on larval Chironomidae, Ephemeroptera, and Plecoptera
Effect of dimerization on the field-induced birefringence in ferrofluids
The magnetic-field-induced birefringence in a ferrofluid composed of spherical cobalt nanoparticles has been studied both experimentally and theoretically. The considerable induced birefringence determined experimentally has been attributed to the formation of chains of nanoparticles. The birefringence has been measured as a function of the external magnetic field and the volume fraction (f) of nanoparticles. It is quadratic in f as opposed to the Faraday effect, which is linear in f. Experimental results agree well with the theoretical model based on a simple density functional approach. For dilute solutions the experimental results can be explained by assuming that only dimers of nanoparticles are formed while the concentration of longer chains is negligible
Optical properties of metallic (III,Mn)V ferromagnetic semiconductors in the infrared to visible range
We report on a study of the ac conductivity and magneto-optical properties of
metallic ferromagnetic (III,Mn)V semiconductors in the infrared to visible
spectrum. Our analysis is based on the successful kinetic exchange model for
(III,Mn)V ferromagnetic semiconductors. We perform the calculations within the
Kubo formalism and treat the disorder effects pertubatively within the Born
approximation, valid for the metallic regime. We consider an eight-band
Kohn-Luttinger model (six valence bands plus two conduction bands) as well as a
ten-band model with additional dispersionless bands simulating
phenomenologically the upper-mid-gap states induced by antisite and
interstitial impurities. These models qualitatively account for
optical-absorption experiments and predict new features in the mid-infrared
Kerr angle and magnetic-circular-dichroism properties as a function of Mn
concentration and free carrier density.Comment: 10 pages, 7 figures, some typos correcte
Second-person pronouns and their relation with nominal forms of address in Late Middle English and Early Modern English personal letters
Synchronic variability in the area of phonetics, phonology, vocabulary, morphology and syntax is a natural feature of any language, including English. The existence of competing variants is in itself a fascinating phenomenon, but it is also a prerequisite for diachronic changes. This volume is a collection of studies which investigate variability from a contemporary and historical perspective, in both native and non-native varieties of English. The topics include Middle English spelling variation, lexical differences between Middle English dialects, Late Middle and Early Modern English forms of address, Middle English negation patterns, the English used by Polish immigrants living in London, lexical fixedness in native and non-native English used by Polish learners, and the phenomenon of phonetic imitation in Polish learners of English. The book should be of interest to anyone interested in English linguistics, especially English phonetics and phonology as well as history of English, historical dialectology and pragmatics.Generally, little attention has been given to the role of selected linguistic and extralinguistic factors in the use of forms of address (Walker 2007). Therefore, the major theoretical concern behind this research is to examine quantitatively and qualitatively, based on selected letters from the CEECS corpus (1998), the influence of social stratification and family relations on the usage of pronominal forms of address. Apart from that, it also analyses the interrelation between second-person pronouns and nominal forms of address in Late Middle English and Early Modern English
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Holomorphology and Drumming Behavior of Western Nearctic Isoperla (Plecoptera)
The holomorphology of ll life stages of 20 western Nearctic Isoperla and one Cascadoperla was studied over the 3-year period 1975-1978. One monotypicgenus new to science, Cascadoperla, is described, and Cascadoperla tricture (Hoppe) designated as the type species. The nymph, adult male and female, and ova are described and illustrated
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The Stoneflies (Plecoptera) of Texas
An illustrated key to the adults and known nymphs of Texas Plecoptera is provided. Species accounts, including geographic distribution within Texas, and biological notes are given.
Of the twenty-seven species of Plecoptera known from Texas, six are new state records. TWo species new to science, Isoperla jewetti and Isoperla coushatta are described.
Taeniopteryx starki Stewart and Szczytko, Zealeuctra arnoldi Ricker and Ross, and Zealeuctra hitei Ricker and Ross are endemic to the Edwards Plateau area of Texas. Two species, Mesocapnia frisoni (Baumam and Gaufin) and Isoperla jewetti New Species are western in origin. The remaining nineteen species (excluding Anacroneuria) are typically eastern species
Direct measure of the exciton formation in quantum wells from time resolved interband luminescence
We present the results of a detailed time resolved luminescence study carried
out on a very high quality InGaAs quantum well sample where the contributions
at the energy of the exciton and at the band edge can be clearly separated. We
perform this experiment with a spectral resolution and a sensitivity of the
set-up allowing to keep the observation of these two separate contributions
over a broad range of times and densities. This allows us to directly evidence
the exciton formation time, which depends on the density as expected from
theory. We also evidence the dominant contribution of a minority of excitons to
the luminescence signal, and the absence of thermodynamical equilibrium at low
densities
Magnetotransport properties of (Ga,Mn)As investigated at low temperature and high magnetic field
Magnetotransport properties of ferromagnetic semiconductor (Ga,Mn)As have
been investigated. Measurements at low temperature (50 mK) and high magnetic
field (<= 27 T) have been employed in order to determine the hole concentration
p = 3.5x10^20 cm ^-3 of a metallic (Ga0.947Mn0.053)As layer. The analysis of
the temperature and magnetic field dependencies of the resistivity in the
paramagnetic region was performed with the use of the above value of p, which
gave the magnitude of p-d exchange energy |N0beta | ~ 1.5 eV.Comment: PDF file, 8 pages, 4 figure
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