Showing 531 - 540 of 733 Items
Combinatorial properties of Thompson's group F
Date: 2004-07-01
Creator: Sean Cleary, Jennifer Taback
Access: Open access
- We study some combinatorial consequences of Blake Fordham's theorems on the word metric of Thompson's group F in the standard two generator presentation. We explore connections between the tree pair diagram representing an element w of F, its normal form in the infinite presentation, its word length, and minimal length representatives of it. We estimate word length in terms of the number and type of carets in the tree pair diagram and show sharpness of those estimates. In addition we explore some properties of the Cayley graph of F with respect to the two generator finite presentation. Namely, we exhibit the form of "dead end" elements in this Cayley graph, and show that it has no "deep pockets". Finally, we discuss a simple method for constructing minimal length representatives for strictly positive or negative words.
Consequences of toxic secondary compounds in nectar for mutualist bees and antagonist butterflies
Date: 2016-10-01
Creator: Patricia L. Jones, Anurag A. Agrawal
Access: Open access
- Attraction of mutualists and defense against antagonists are critical challenges for most organisms and can be especially acute for plants with pollinating and non-pollinating flower visitors. Secondary compounds in flowers have been hypothesized to adaptively mediate attraction of mutualists and defense against antagonists, but this hypothesis has rarely been tested. The tissues of milkweeds (Asclepias spp.) contain toxic cardenolides that have long been studied as chemical defenses against herbivores. Milkweed nectar also contains cardenolides, and we have examined the impact of manipulating cardenolides in nectar on the foraging choices of two flower visitors: generalist bumble bees, Bombus impatiens, which are mutualistic pollinators, and specialist monarch butterflies, Danaus plexippus, which are herbivores as larvae and ineffective pollinators as adults. Although individual bumble bees in single foraging bouts showed no avoidance of cardenolides at the highest natural concentrations reported for milkweeds, a pattern of deterrence did arise when entire colonies were allowed to forage for several days. Monarch butterflies were not deterred by the presence of cardenolides in nectar when foraging from flowers, but laid fewer eggs on plants paired with cardenolide-laced flowers compared to controls. Thus, although deterrence of bumble bees by cardenolides may only occur after extensive foraging, a primary effect of nectar cardenolides appears to be reduction of monarch butterfly oviposition.
Surface symmetries and PSL2(p)
Date: 2007-05-01
Creator: Murad Özaydin, Charlotte Simmons, Jennifer Taback
Access: Open access
- We classify, up to conjugacy, all orientation-preserving actions of PSL2(p) on closed connected orientable surfaces with spherical quotients. This classification is valid in the topological, PL, smooth, conformal, geometric and algebraic categories and is related to the Inverse Galois Problem. © 2006 American Mathematical Society.
Social Learning Strategies: Bridge-Building between Fields
Date: 2018-07-01
Creator: Rachel L. Kendal, Neeltje J. Boogert, Luke Rendell, Kevin N. Laland, Mike, Webster, Patricia L. Jones
Access: Open access
- While social learning is widespread, indiscriminate copying of others is rarely beneficial. Theory suggests that individuals should be selective in what, when, and whom they copy, by following 'social learning strategies’ (SLSs). The SLS concept has stimulated extensive experimental work, integrated theory, and empirical findings, and created impetus to the social learning and cultural evolution fields. However, the SLS concept needs updating to accommodate recent findings that individuals switch between strategies flexibly, that multiple strategies are deployed simultaneously, and that there is no one-to-one correspondence between psychological heuristics deployed and resulting population-level patterns. The field would also benefit from the simultaneous study of mechanism and function. SLSs provide a useful vehicle for bridge-building between cognitive psychology, neuroscience, and evolutionary biology.
Erratum: Context-dependent protein stabilization by methionine-to- leucine substitution shown in T4 lysozyme (Protein Science (November 3, 1998) 7:3 (772))
Date: 1998-01-01
Creator: L. A. Lipscomb, N. C. Gassner, S. D. Snow, A. M. Eldridge, W. A., Baase, D. L. Drew, B. W. Matthews
Access: Open access
Mitochondrial genotype influences the response to cold stress in the European green crab, Carcinus maenas
Date: 2019-01-01
Creator: Aidan F. Coyle, Erin R. Voss, Carolyn K. Tepolt, David B. Carlon
Access: Open access
- Hybrid zones provide natural experiments in recombination within and between genomes that may have strong effects on organismal fitness. On the East Coast of North America, two distinct lineages of the European green crab (Carcinus maenas) have been introduced in the last two centuries. These two lineages with putatively different adaptive properties have hybridized along the coast of the eastern Gulf of Maine, producing new nuclear and mitochondrial combinations that show clinal variation correlated with water temperature. To test the hypothesis that mitochondrial or nuclear genes have effects on thermal tolerance, we first measured the response to cold stress in crabs collected throughout the hybrid zone, then sequenced the mitochondrial CO1 gene and two nuclear single nucleotide polymorphisms (SNPs) representative of nuclear genetic lineage. Mitochondrial haplotype had a strong association with the ability of crabs to right themselves at 4.5°C that was sex specific: haplotypes originally from northern Europe gave male crabs an advantage while there was no haplotype effect on righting in female crabs. By contrast, the two nuclear SNPs that were significant outliers in a comparison between northern and southern C. maenas populations had no effect on righting response at low temperature. These results add C. maenas to the shortlist of ectotherms in which mitochondrial variation has been shown to affect thermal tolerance, and suggest that natural selection is shaping the structure of the hybrid zone across the Gulf of Maine. Our limited genomic sampling does not eliminate the strong possibility that mito-nuclear co-adaptation may play a role in the differences in thermal phenotypes documented here. Linkage between mitochondrial genotype and thermal tolerance suggests a role for local adaptation in promoting the spread of invasive populations of C. maenas around the world.
Semileptonic branching fractions of charged and neutral B mesons
Date: 1994-01-01
Creator: M. Athanas, W. Brower, G. Masek, H. P. Paar, J., Gronberg, R. Kutschke, S. Menary, R. J. Morrison, S. Nakanishi, H. N. Nelson, T. K. Nelson, C. Qiao, J. D. Richman, A. Ryd, H. Tajima, D. Sperka, M. S. Witherell, R. Balest, K. Cho, W. T. Ford, D. R. Johnson, K. Lingel, M. Lohner, P. Rankin, J. G. Smith, J. P. Alexander, C. Bebek, K. Berkelman, K. Bloom, T. E. Browder, D. G. Cassel
Access: Open access
- An examination of leptons in (4S) events tagged by reconstructed B meson decays yields semileptonic branching fractions of b-=(10.1±1.8±1. 5)% for charged and b0=(10.9±0.7±1.1)% for neutral B mesons. This is the first measurement for charged B mesons. Assuming equality of the charged and neutral semileptonic widths, the ratio b-b0=0.93±0.18±0.12 is equivalent to the ratio of lifetimes. © 1994 The American Physical Society.
Measurement of two-photon production of the χc2
Date: 1994-01-01
Creator: J. Dominick, S. Sanghera, V. Shelkov, T. Skwarnicki, R., Stroynowski, I. Volobouev, P. Zadorozhny, M. Artuso, D. He, M. Goldberg, N. Horwitz, R. Kennett, G. C. Moneti, F. Muheim, Y. Mukhin, S. Playfer, Y. Rozen, S. Stone, M. Thulasidas, G. Vasseur, G. Zhu, J. Bartelt, S. E. Csorna, Z. Egyed, V. Jain, P. Sheldon, D. S. Akerib, B. Barish, M. Chadha, S. Chan, D. F. Cowen
Access: Open access
- The CLEO II detector is used to search for the production of χc2 states in two-photon interactions. We use the signature χc2→γJ/ ψ→γl+l- with l=e,μ. Using 1.49 fb-1 of data taken with beam energies near 5.29 GeV, the two-photon width of the χc2 is determined to be Γ(χc2→γγ)=1.08±0.30(stat)±0.26(syst) keV, in agreement with predictions from perturbative QCD. © 1994 The American Physical Society.
Isolation of nine microsatellite loci in Dolichogenidea homoeosomae (Hymenoptera) a parasitoid of the sunflower moth Homoeosoma electellum (Lepidoptera)
Date: 2006-03-01
Creator: Vladimir Douhovnikoff, Caterina Nerney, George K. Roderick, Craig H. Newton, Stephen C., Welter
Access: Open access
- Nine microsatellite loci were isolated from the insect Dolichogenidea homoeosomae (Hymenoptera: Braconidae), an important parasitoid of the sunflower moth Homosoeosoma electellum (Lepidoptera: Pyralidae), and assayed for polymorphism. All nine loci were polymorphic within the five populations tested, with two to 14 alleles per locus. Expected and observed heterozygosities ranged from 0.39 to 0.90 and 0.25 to 0.72 respectively. These are the first microsatellite primers developed for D. homeosomae and will be useful for studies of population dynamics and connectivity. © 2006 Blackwell Publishing Ltd.
Level-rank duality of untwisted and twisted D-branes of the over(so, ̂) (N)K WZW model
Date: 2007-12-24
Creator: Stephen G. Naculich, Benjamin H. Ripman
Access: Open access
- We analyze the level-rank duality of untwisted and ε-twisted D-branes of the over(so, ̂) (N)K WZW model. Untwisted D-branes of over(so, ̂) (N)K are characterized by integrable tensor and spinor representations of over(so, ̂) (N)K. Level-rank duality maps untwisted over(so, ̂) (N)K D-branes corresponding to (equivalence classes of ) tensor representations onto those of over(so, ̂) (K)N. The ε-twisted D-branes of over(so, ̂) (2 n)2 k are characterized by (a subset of ) integrable tensor and spinor representations of over(so, ̂) (2 n - 1)2 k + 1. Level-rank duality maps spinor ε-twisted over(so, ̂) (2 n)2 k D-branes onto those of over(so, ̂) (2 k)2 n. For both untwisted and ε-twisted D-branes, we prove that the spectrum of an open string ending on these D-branes is isomorphic to the spectrum of an open string ending on the level-rank-dual D-branes. © 2007 Elsevier B.V. All rights reserved.