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Natural Resources and Conservation
Nebraska Cooperative Fish and Wildlife Research Unit: Staff Publications
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Articles 151 - 160 of 160
Full-Text Articles in Physical Sciences and Mathematics
Extensions Of Local Domains With Trivial Generic Fiber, William Heinzer, Christel Rotthaus, Sylvia Wiegand
Extensions Of Local Domains With Trivial Generic Fiber, William Heinzer, Christel Rotthaus, Sylvia Wiegand
Nebraska Cooperative Fish and Wildlife Research Unit: Staff Publications
We consider injective local maps from a local domain R to a local domain S such that the generic fiber of the inclusion map R -> S is trivial, that is P R (0) for every nonzero prime ideal P of S. We present several examples of injective local maps involving power series that have or fail to have this property. For an extension R -> S having this property, we give some results on the dimension of S; in some cases we show dim S = 2 and in some cases dim S = 1.
Climate-Induced Forest Dieback As An Emergent Global Phenomenon, Craig Allen, David D. Breshears
Climate-Induced Forest Dieback As An Emergent Global Phenomenon, Craig Allen, David D. Breshears
Nebraska Cooperative Fish and Wildlife Research Unit: Staff Publications
An organized oral session at the annual meeting of the Ecological Society of America in San Jose, Calif., posed this question: Is climate-induced drought stress triggering increasing rates and unusual patterns of forest die-off at a global scale? Twenty-nine researchers representing five continents reported on patterns, mechanisms, and projections of forest mortality.
Factors Affecting Regional Variation In Growth Of Channel Catfish, Bart W. Durham, Kevin L. Pope, Gene R. Wilde
Factors Affecting Regional Variation In Growth Of Channel Catfish, Bart W. Durham, Kevin L. Pope, Gene R. Wilde
Nebraska Cooperative Fish and Wildlife Research Unit: Staff Publications
We related the length at age of channel catfish Ictalurus punctatus, an indirect measure of growth, to three climatic and five morphoedaphic variables in 144 Texas reservoirs. Growth of channel catfish ages 3 through 6 was negatively related to longitude, a factor that explained as much as 34% of the variation in length at age. Channel catfish length at age was not significantly related to latitude, conductivity, morphoedaphic index, mean depth, and maximum depth in all age-classes. Among age-7 channel catfish, length at age was positively related to reservoir area, which explained 35% of the variation in growth. A …
The Use Of Discontinuities And Functional Groups To Assess Relative Resilience In Complex Systems, Craig R. Allen, L. Gunderson, A. R. Johnson
The Use Of Discontinuities And Functional Groups To Assess Relative Resilience In Complex Systems, Craig R. Allen, L. Gunderson, A. R. Johnson
Nebraska Cooperative Fish and Wildlife Research Unit: Staff Publications
It is evident when the resilience of a system has been exceeded and the system qualitatively changed. However, it is not clear how to measure resilience in a system prior to the demonstration that the capacity for resilient response has been exceeded. We argue that self-organizing human and natural systems are structured by a relatively small set of processes operating across scales in time and space. These structuring processes should generate a discontinuous distribution of structures and frequencies, where discontinuities mark the transition from one scale to another. Resilience is not driven by the identity of elements of a system, …
Intermediate Rings Between A Local Domain And Its Completion, Ii, William Heinzer, Christel Rotthaus, Sylvia Wiegand
Intermediate Rings Between A Local Domain And Its Completion, Ii, William Heinzer, Christel Rotthaus, Sylvia Wiegand
Nebraska Cooperative Fish and Wildlife Research Unit: Staff Publications
We present results connecting flatness of extension rings to the Noetherian property for certain intermediate rings between an excellent normal local domain and its completion. We consider conditions for these rings to have Cohen-Macaulay formal fibers. We also present several examples illustrating these results.
Yellow Jackets (Vespula Spp.) Disperse Trillium (Spp.) Seeds In Eastern North America, Jennifer A. Zettler, Timonthy P. Spira, Craig R. Allen
Yellow Jackets (Vespula Spp.) Disperse Trillium (Spp.) Seeds In Eastern North America, Jennifer A. Zettler, Timonthy P. Spira, Craig R. Allen
Nebraska Cooperative Fish and Wildlife Research Unit: Staff Publications
Approximately 70 plant families worldwide have ant-dispersed seeds (myrmecochory). In this putative ant-plant mutualism, ants are attracted to and disperse seeds that have a lipid-rich elaiosome. We observed yellow jackets (Vespula spp.) dispersing seeds of three elaiosome-bearing species-Trillium cuneatum, T. undulatum and T catesbaei-in the Blue Ridge Mountains of North Carolina and South Carolina. Moreover, we estimated the mean distance yellow jackets dispersed seeds of T. cuneatum by placing intact fruits on index cards and recovering dispersed seeds on sheets placed on the ground surface. Of the seeds presented, 41% were recovered and the average dispersal distance …
Intermediate Rings Between A Local Domain And Its Completion, William Heinzer, Christel Rotthaus, Sylvia Wiegand
Intermediate Rings Between A Local Domain And Its Completion, William Heinzer, Christel Rotthaus, Sylvia Wiegand
Nebraska Cooperative Fish and Wildlife Research Unit: Staff Publications
We consider the structure of certain intermediate domains between a local Noetherian domain Rand an ideal-adic completion R* of R that arise as the intersection of R* with a field containing R. In the case where the intersection domain A can be expressed as a directed union of localized polynomial extension rings of R, the computation of A is easier. We examine conditions for this to happen. We also present examples to motivate and illustrate the concepts considered.
Drought-Induced Shift Of A Forest–Woodland Ecotone: Rapid Landscape Response To Climate Variation, Craig Allen, David D. Breshears
Drought-Induced Shift Of A Forest–Woodland Ecotone: Rapid Landscape Response To Climate Variation, Craig Allen, David D. Breshears
Nebraska Cooperative Fish and Wildlife Research Unit: Staff Publications
In coming decades, global climate changes are expected to produce large shifts in vegetation distributions at unprecedented rates. These shifts are expected to be most rapid and extreme at ecotones, the boundaries between ecosystems, particularly those in semiarid landscapes. However, current models do not adequately provide for such rapid effects—particularly those caused by mortality—largely because of the lack of data from field studies. Here we report the most rapid landscape-scale shift of a woody ecotone ever documented: in northern New Mexico in the 1950s, the ecotone between semiarid ponderosa pine forest and pinon– juniper woodland shifted extensively (2 km or …
Idealwise Algebraic Independence For Elements Of The Completion Of A Local Domain, William Heinzer, Christel Rotthaus, Sylvia Wiegand
Idealwise Algebraic Independence For Elements Of The Completion Of A Local Domain, William Heinzer, Christel Rotthaus, Sylvia Wiegand
Nebraska Cooperative Fish and Wildlife Research Unit: Staff Publications
Over the past forty years many examples in commutative algebra have been constructed using the following principle: Let k be a field, let S k[xl Xn]x,xn) be a localized polynomial ring over k, and let a be an ideal in the completion S of S such that the associated prims of a are in the generic formal fiber of S; that is, p N S (0) for each p Ass(S/a):. Then S embeds in S/a, the fraction field Q(S) of S embeds in the fraction ring of S/a, and for certain choices of a, the intersection D Q(S) f3 (S/a) …
Finitely Generated Modules Over Bezout Ringsrwiegand@Unl.Edu, Roger Wiegand, Sylvia Wiegand
Finitely Generated Modules Over Bezout Ringsrwiegand@Unl.Edu, Roger Wiegand, Sylvia Wiegand
Nebraska Cooperative Fish and Wildlife Research Unit: Staff Publications
Let R be a Bezout ring (a commutative ring in which all finitely generated ideals are principal), and let M be a finitely generated R -module. We will study questions of the following sort: (A) If every localization of M can be generated by n elements, can M itself be generated by n elements? (B) If M 0 R m = Rn for some m, n, is Af necessarily free? (C) If every localization of M has an element with zero annihilator, does M itself have such an element? We will answer these and related questions for various familiar classes …