The Experts below are selected from a list of 243 Experts worldwide ranked by ideXlab platform
Giovanni B Bachelet - One of the best experts on this subject based on the ideXlab platform.
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electrons and phonons in the ternary alloy caal 2 x si x as a function of composition
Physical Review B, 2005Co-Authors: Matteo Giantomassi, Lilia Boeri, Giovanni B BacheletAbstract:We report a detailed first-principles study of the structural, electronic, and vibrational properties of the superconducting ${\mathrm{C}}_{32}$ phase of the ternary alloy ${\mathrm{CaAl}}_{2\ensuremath{-}x}{\mathrm{Si}}_{x}$, both in the Experimental Range $0.6\ensuremath{\leqslant}x\ensuremath{\leqslant}1.2$, for which the alloy has been synthesized, and in the theoretical limits of high aluminum and high silicon concentration. Our results indicate that, in the Experimental Range, the dependence of the electronic bands on composition is well described by a rigid-band model, which breaks down outside this Range. Such a breakdown, in the (theoretical) limit of high aluminum concentration, is connected to the appearance of vibrational instabilities and results in important differences between ${\mathrm{CaAl}}_{2}$ and ${\mathrm{MgB}}_{2}$. Unlike ${\mathrm{MgB}}_{2}$, the interlayer band and the out-of-plane phonons play a major role on the stability and superconductivity of CaAlSi and related ${\mathrm{C}}_{32}$ intermetallic compounds.
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Electrons and phonons in the ternary alloy CaAl 2 − x Si x as a function of composition
Physical Review B, 2005Co-Authors: Matteo Giantomassi, Lilia Boeri, Giovanni B BacheletAbstract:We report a detailed first-principles study of the structural, electronic, and vibrational properties of the superconducting ${\mathrm{C}}_{32}$ phase of the ternary alloy ${\mathrm{CaAl}}_{2\ensuremath{-}x}{\mathrm{Si}}_{x}$, both in the Experimental Range $0.6\ensuremath{\leqslant}x\ensuremath{\leqslant}1.2$, for which the alloy has been synthesized, and in the theoretical limits of high aluminum and high silicon concentration. Our results indicate that, in the Experimental Range, the dependence of the electronic bands on composition is well described by a rigid-band model, which breaks down outside this Range. Such a breakdown, in the (theoretical) limit of high aluminum concentration, is connected to the appearance of vibrational instabilities and results in important differences between ${\mathrm{CaAl}}_{2}$ and ${\mathrm{MgB}}_{2}$. Unlike ${\mathrm{MgB}}_{2}$, the interlayer band and the out-of-plane phonons play a major role on the stability and superconductivity of CaAlSi and related ${\mathrm{C}}_{32}$ intermetallic compounds.
Matteo Giantomassi - One of the best experts on this subject based on the ideXlab platform.
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electrons and phonons in the ternary alloy caal 2 x si x as a function of composition
Physical Review B, 2005Co-Authors: Matteo Giantomassi, Lilia Boeri, Giovanni B BacheletAbstract:We report a detailed first-principles study of the structural, electronic, and vibrational properties of the superconducting ${\mathrm{C}}_{32}$ phase of the ternary alloy ${\mathrm{CaAl}}_{2\ensuremath{-}x}{\mathrm{Si}}_{x}$, both in the Experimental Range $0.6\ensuremath{\leqslant}x\ensuremath{\leqslant}1.2$, for which the alloy has been synthesized, and in the theoretical limits of high aluminum and high silicon concentration. Our results indicate that, in the Experimental Range, the dependence of the electronic bands on composition is well described by a rigid-band model, which breaks down outside this Range. Such a breakdown, in the (theoretical) limit of high aluminum concentration, is connected to the appearance of vibrational instabilities and results in important differences between ${\mathrm{CaAl}}_{2}$ and ${\mathrm{MgB}}_{2}$. Unlike ${\mathrm{MgB}}_{2}$, the interlayer band and the out-of-plane phonons play a major role on the stability and superconductivity of CaAlSi and related ${\mathrm{C}}_{32}$ intermetallic compounds.
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Electrons and phonons in the ternary alloy CaAl 2 − x Si x as a function of composition
Physical Review B, 2005Co-Authors: Matteo Giantomassi, Lilia Boeri, Giovanni B BacheletAbstract:We report a detailed first-principles study of the structural, electronic, and vibrational properties of the superconducting ${\mathrm{C}}_{32}$ phase of the ternary alloy ${\mathrm{CaAl}}_{2\ensuremath{-}x}{\mathrm{Si}}_{x}$, both in the Experimental Range $0.6\ensuremath{\leqslant}x\ensuremath{\leqslant}1.2$, for which the alloy has been synthesized, and in the theoretical limits of high aluminum and high silicon concentration. Our results indicate that, in the Experimental Range, the dependence of the electronic bands on composition is well described by a rigid-band model, which breaks down outside this Range. Such a breakdown, in the (theoretical) limit of high aluminum concentration, is connected to the appearance of vibrational instabilities and results in important differences between ${\mathrm{CaAl}}_{2}$ and ${\mathrm{MgB}}_{2}$. Unlike ${\mathrm{MgB}}_{2}$, the interlayer band and the out-of-plane phonons play a major role on the stability and superconductivity of CaAlSi and related ${\mathrm{C}}_{32}$ intermetallic compounds.
Kathryn L. Purcell - One of the best experts on this subject based on the ideXlab platform.
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Long-term avian research at the San Joaquin Experimental Range: recommendations for monitoring and managing oak woodlands
Forest Ecology and Management, 2011Co-Authors: Kathryn L. PurcellAbstract:Abstract Experimental forests and Ranges are living laboratories that provide opportunities for conducting scientific research and transferring research results to partners and stakeholders. They are invaluable for their long-term data and capacity to foster collaborative, interdisciplinary research. The San Joaquin Experimental Range (SJER) was established to develop appropriate land management practices on foothill Rangelands in California. SJER has a long and rich history of avian research. Natural history observations recorded since 1935 demonstrate that oak woodlands are one of the most diverse habitat types in North America. Early avian studies focused on California quail (Callipepla californica) as a game species and led to insights on quail diet and habitat requirements. Starting in the late 1970s, the focus of avian research shifted to methods for detecting changes in wildlife populations over time and response to management practices. This research has led to important recommendations for implementing bird monitoring programs. Using data collected on bird numbers, in conjunction with monitoring reproductive success of all species, recent studies have examined life history strategies, source–sink dynamics, the effects of livestock grazing, and the impacts of an invasive species on native cavity-nesting species. We are currently in the process of examining population trends and predicting the effects of climate change using long-term data. SJER continues to provide unique opportunities for research and educational activities that increase our understanding of the foothill oak woodlands of California.
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Nest-site habitat of cavity-nesting birds at the San Joaquin Experimental Range
2008Co-Authors: Kathryn L. Purcell, Jared VernerAbstract:Detailed information about the nesting habitats of birds, including those needed for successful nesting, can provide a better understanding of the ecological factors that permit coexistence of different species and may aid in conservation efforts. From 1989 through 1994, we studied the nesting habitat of secondary cavity-nesting birds in oak woodlands at the San Joaquin Experimental Range, Madera County, CA. We measured habitat surrounding nests and examined similarities and differences in nesting habitat used by eight species to evaluate overlap in nesting habitat use and possible competition. Nesting habitat of Bewick's Wrens (Thryomanes bewickii) was unique among the species studied. Their nests were the lowest and located in the densest habitat on the steepest slopes where interior live oaks (Quercus wislizenii) were abundant. Nesting habitat was similar among European Starlings (Sturnus vulgaris), Western Bluebirds (Sialia mexicana), and Violet-green Swallows (Tachycineta bicolor). These species all nested in open areas with the highest density of blue oaks (Quercus douglasii), the lowest densities of live oaks and snags, and the lowest basal area of trees. Nests of White-breasted Nuthatches (Sitta carolinensis) were similar to the above three species, differing only in being lower compared to nests of European Starlings. Ash-throated Flycatcher (Myiarchus cinerascens) nesting habitat was characterized by dense stands of trees with a high density of live oaks and snags. Oak Titmouse (Baeolophus inornatus) nests were low and located in high-density stands of live oaks on steep slopes. House Wrens (Troglodytes aedon) nested in dense stands of trees. Successful Ash-throated Flycatcher and Oak Titmouse nests had higher basal area of live trees compared to unsuccessful nests and, compared to other species, habitat surrounding their nests had high basal area. European Starling nests were highest, and nests located high in trees had higher nest survival. Consequently, these three species tended to select nest sites in habitats where they had higher nest success. We recommend management activities that maintain habitat diversity, including areas that differ in tree species composition and density, to promote species diversity.
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Factors Affecting the Abundance and Distribution of European Starlings at the San Joaquin Experimental Range 1
2002Co-Authors: Kathryn L. Purcell, Jared Verner, Sylvia R. MoriAbstract:We examined population trends and factors related to the abundance and presence of European starlings (Sturnus vulgaris) at the San Joaquin Experimental Range in the foothills of the western Sierra Nevada, 31 km east of Madera, California. Starlings first appeared there in low numbers in the late 1960s and are now abundant breeders. Simple models examining trends in starling numbers and presence/absence using point-counting data from 210 counting stations from 1985 through 2000 showed significantly increasing yearly trends in starling abundance and distribution. The yearly trend in abundance, however, became nonsignificant when weather patterns were included. Similarly, starling presence/absence showed an increasing trend over years, but the trend became sinusoidal when weather and habitat variables were included. Our data show that spurious results may occur when appropriate explanatory variables are not included in the analysis of population trends. Starlings were more abundant after years with cool summers, warm, wet winters, and on early and late count dates. Starling presence was related to habitat attributes generally considered necessary for foraging—level, open woodlands with fairly well-developed, accessible soil. Summer is the time of year when resources are most limiting for starlings in the foothill oak woodlands, as they primarily forage on arthropods in moist soils. Cool summers and wet winters permit the soils, especially swales, to remain moist and productive longer, thereby promoting higher starling abundance. Research is needed on the potential effects of starlings on native species of birds and the conservation and production values of the ecosystems they have invaded.
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Bird Communities in Grazed and Ungrazed Oak-Pine Woodlands at the San Joaquin Experimental Range
1997Co-Authors: Jared Verner, Kathryn L. Purcell, Jennifer G. TurnerAbstract:Ten years of spot-mapping censuses in grazed and ungrazed plots at the San Joaquin Experimental Range, Madera Co., California, indicate likely changes in abundance of several bird species. Data do not, however, indicate that any species is in jeopardy as a result of grazing in the foothill woodlands. Brown-headed cowbirds are probably more abundant in the woodlands with cattle than without cattle, but we have no evidence that cowbird nest parasitism is a threat to any host species. Finally, the European starling's possible impact on native cavity-nesting species is uncertain, but we suspect it is significant for some species. I n 1934, the USDA Forest Service purchased private ranchlands in foothill woodlands of the western Sierra Nevada to establish the San Joaquin Experimental Range (SJER). The stated objective of this acquisition was to undertake Range research in California, which "...is most important for the stability of a large industry and for the maintenance of public values to be rendered by grazing lands" (Kotok 1933). Foremost among the public values of interest at the time were a viable livestock industry, sustainable water resources, and Rangeland production. Other values were also recognized, including the rich wildlife communities that occur in the foothill woodlands. Publications based on studies of a wide variety of species in all vertebrate classes at SJER began to appear in the late 1930's and early 1940's (Duncan and Coon 1985). The primary objective of the present study was to evaluate spot mapping as a method to estimate the densities of breeding bird populations. Secondarily, we hoped to attain some insights into possible effects of long-term grazing on bird communities in oak-pine woodlands of the western Sierra Nevada. This second objective was possible only because a 32-ha parcel was set aside in 1934 and has been excluded from livestock grazing ever since. In this paper, we compare the breeding bird community in this ungrazed parcel with that in a grazed study area of equal size. Although the study lacks replication because only one ungrazed parcel was available, we nonetheless believe that some useful biological inferences can be drawn from the results.
Lilia Boeri - One of the best experts on this subject based on the ideXlab platform.
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electrons and phonons in the ternary alloy caal 2 x si x as a function of composition
Physical Review B, 2005Co-Authors: Matteo Giantomassi, Lilia Boeri, Giovanni B BacheletAbstract:We report a detailed first-principles study of the structural, electronic, and vibrational properties of the superconducting ${\mathrm{C}}_{32}$ phase of the ternary alloy ${\mathrm{CaAl}}_{2\ensuremath{-}x}{\mathrm{Si}}_{x}$, both in the Experimental Range $0.6\ensuremath{\leqslant}x\ensuremath{\leqslant}1.2$, for which the alloy has been synthesized, and in the theoretical limits of high aluminum and high silicon concentration. Our results indicate that, in the Experimental Range, the dependence of the electronic bands on composition is well described by a rigid-band model, which breaks down outside this Range. Such a breakdown, in the (theoretical) limit of high aluminum concentration, is connected to the appearance of vibrational instabilities and results in important differences between ${\mathrm{CaAl}}_{2}$ and ${\mathrm{MgB}}_{2}$. Unlike ${\mathrm{MgB}}_{2}$, the interlayer band and the out-of-plane phonons play a major role on the stability and superconductivity of CaAlSi and related ${\mathrm{C}}_{32}$ intermetallic compounds.
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Electrons and phonons in the ternary alloy CaAl 2 − x Si x as a function of composition
Physical Review B, 2005Co-Authors: Matteo Giantomassi, Lilia Boeri, Giovanni B BacheletAbstract:We report a detailed first-principles study of the structural, electronic, and vibrational properties of the superconducting ${\mathrm{C}}_{32}$ phase of the ternary alloy ${\mathrm{CaAl}}_{2\ensuremath{-}x}{\mathrm{Si}}_{x}$, both in the Experimental Range $0.6\ensuremath{\leqslant}x\ensuremath{\leqslant}1.2$, for which the alloy has been synthesized, and in the theoretical limits of high aluminum and high silicon concentration. Our results indicate that, in the Experimental Range, the dependence of the electronic bands on composition is well described by a rigid-band model, which breaks down outside this Range. Such a breakdown, in the (theoretical) limit of high aluminum concentration, is connected to the appearance of vibrational instabilities and results in important differences between ${\mathrm{CaAl}}_{2}$ and ${\mathrm{MgB}}_{2}$. Unlike ${\mathrm{MgB}}_{2}$, the interlayer band and the out-of-plane phonons play a major role on the stability and superconductivity of CaAlSi and related ${\mathrm{C}}_{32}$ intermetallic compounds.
Guillermo E. Defossé - One of the best experts on this subject based on the ideXlab platform.
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Length and Timing of Grazing on Postburn Productivity of Two Bunchgrasses in an Idaho Experimental Range
International Journal of Wildland Fire, 1998Co-Authors: Stephen C. Bunting, Ronald Robberecht, Guillermo E. DefosséAbstract:Plant mortality and productivity in semiarid grasslands may be affected by the length of time grazing is excluded during the postfire regeneration period. The degree of grazing tolerance for the semiarid bunchgrass species, Festuca idahoensis and Agropyron spicatum, exposed to fire, and how the variation in grazing tolerance was affected by the length of time allowed for undisturbed plant regeneration after fire, were central questions addressed in this study. We examined the degree of plant mortality and productivity that resulted from the interaction of fire and grazing. Plants exposed to fire alone, i.e., without subsequent defoliation, exhibited low plant mortality, although culm production was reduced relative to unburned plants. An early-season-defoliation treatment after fire resulted in the plant mortality as high as 50% for Festuca and 70% for Agropyron bunchgrasses. Plant height and the number of vegetative and reproductive culms were also most affected by this defoliation treatment. These detrimental effects were lessened when defoliation was delayed by one growing season after the fire. Although our results suggest that one growing season seems to be enough for both species to recover after the fire, more studies will be necessary to confirm these trends, and induce changes in current grazing management policies.
