Showing 751 - 760 of 2039 Items
Large N universality of the two-dimensional Yang-Mills string
Date: 1995-07-17
Creator: Michael Crescimanno
Stephen G. Naculich
Howard J. Schnitzer
Access: Open access
- We exhibit the gauge-group independence ("universality") of all normalized non-intersecting Wilson loop expectation values in the large N limit of two-dimensional Yang-Mills theory. This universality is most easily understood via the string theory reformulation of these gauge theories. By constructing an isomorphism between the string maps contributing to normalized Wilson loop expectation values in the different theories, we prove the large N universality of these observables on any surface. The string calculation of the Wilson loop expectation value on the sphere also leads to an indication of the large N phase transition separating strong- and weak-coupling phases. © 1995.
The Effects of Host Plant Species and Plant Quality on Growth and Development in the Meadow Spittlebug (Philaenus spumarius) on Kent Island in the Bay of Fundy
Date: 2020-03-01
Creator: Zoe M. Wood
Patricia L. Jones
Access: Open access
- Philaenus spumarius (Meadow Spittlebug, Homoptera: Cercopoidea) is a cosmopolitan generalist insect that feeds on a wide repertoire of host plants in the field. We studied density and growth of Meadow Spittlebugs on a range of host plants on Kent Island, a boreal island in the Bay of Fundy, NB, Canada. The highest spittlebug densities were on Cirsium arvense (Canadian Thistle), although spittlebugs had larger body sizes on Solidago rugosa (Rough-stemmed Goldenrod) and Anaphalis margaritacea (Pearly Everlasting). We fertilized plots of Rough-stemmed Goldenrod in the field over 3 weeks to examine the effects of plant quality on development of Meadow Spittlebugs. Following fertilization, there were fewer nymphs present in fertilized plots than in unfertilized plots, indicating faster nymph maturation to adulthood on fertilized plants. This study offers an initial report of the host plants used by Meadow Spittlebugs in northeastern boreal habitat, variation in density and performance of the species on a range of host plants, and the effects of plant fertilization on spittlebug life history.
Two-photon production of charged pion and kaon pairs
Date: 1994-01-01
Creator: J. Dominick
M. Lambrecht
S. Sanghera
V. Shelkov
T., Skwarnicki
R. Stroynowski
I. Volobouev
G. Wei
P. Zadorozhny
M. Artuso
M. Goldberg
D. He
N. Horwitz
R. Kennett
R. Mountain
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
K. Kinoshita
K. W. Edwards
M. Ogg
Access: Open access
- A measurement of the cross section for the combined two-photon production of charged pion and kaon pairs is performed using 1.2 fb-1 of data collected by the CLEO II detector at the Cornell Electron Storage Ring. The cross section is measured at invariant masses of the two-photon system between 1.5 and 5.0 GeV/c2, and at scattering angles more than 53° away from the γγ collision axis in the γγ center-of-mass frame. The large background of leptonic events is suppressed by utilizing the CsI calorimeter in conjunction with the muon chamber system. The reported cross section is compared with leading order QCD models as well as previous experiments. Although the functional dependence of the measured cross section disagrees with leading order QCD at small values of the two-photon invaraint mass, the data show qualitatively a transition to perturbative behavior at an invariant mass of approximately 2.5 GeV/c2. © 1994 The American Physical Society.
Clonal growth: Invasion or stability? A comparative study of clonal architecture and diversity in native and introduced lineages of Phragmites australis (Poaceae)
Date: 2014-09-01
Creator: Vladimir Douhovnikoff
Eric L.G. Hazelton
Access: Open access
- Premise of the study: The characteristics of clonal growth that are advantageous in invasive plants can also result in native plants’ ability to resist invasion. In Maine, we compared the clonal architecture and diversity of an invasive lineage (introduced Phragmites) and a noninvasive lineage (native Phragmites) present in much of North America. This study is the fi rst on standscale diversity using a sample size and systematic spatial-sampling scheme adequate for characterizing clonal structure in Phragmites. Our questions included: (1) Does the structure and extent of clonal growth suggest that the potential for clonal growth contributes to the invasiveness of the introduced lineage? (2) Is clonal growth common in the native lineage, acting as a possible source of ecological resistance and resilience?
Clonal diversity in an expanding community of Arctic Salix spp. and a model for recruitment modes of arctic plants
Date: 2010-11-01
Creator: Vladimir Douhovnikoff
Gregory R. Goldsmith
Ken D. Tape
Cherrie Huang
Nadine, Sur
M. Syndonia Bret-Harte
Access: Open access
- Rapid climate change in arctic environments is leading to a widespread expansion in woody deciduous shrub populations. However, little is known about the reproductive, dispersal, and establishment mechanisms associated with shrub expansion. It is assumed that harsh environmental conditions impose limitations on plant sexual reproduction in the Arctic, such that population survival and expansion is predominately a function of clonal recruitment. We present contrary evidence from microsatellite genetic data suggesting the prevalence of recruitment by seed. Further, we present a conceptual model describing modes of recruitment in relation to the abiotic environment. Climate change may be alleviating abiotic stress so that resources are available for more frequent recruitment by seed. Such changes have widespread implications for ecosystem structure and functioning, including species composition, wildlife habitat, biogeochemical cycling, and surface energy balance. © 2010 Regents of the University of Colorado.
Measurement of the branching fraction scrB(τ-→h- →π0ντ)
Date: 1994-01-01
Creator: M. Artuso
M. Goldberg
D. He
N. Horwitz
R., Kennett
R. Mountain
G. C. Moneti
F. Muheim
Y. Mukhin
S. Playfer
Y. Rozen
S. Stone
M. Thulasidas
G. Vasseur
X. Xing
G. Zhu
J. Bartelt
S. E. Csorna
Z. Egyed
V. Jain
K. Kinoshita
B. Barish
M. Chadha
S. Chan
D. F. Cowen
G. Eigen
J. S. Miller
C. O'Grady
J. Urheim
A. J. Weinstein
D. Acosta
Access: Open access
- Using data from the CLEO II detector at the Cornell Electron Storage Ring, we measure scrB(τ-→h-π0ντ) where h- refers to either π- or K-. We use three different methods to measure this branching fraction. The combined result is scrB(τ-→h-π0ντ)=0.2587±0. 0012±0.0042, in good agreement with standard model predictions. © 1994 The American Physical Society.
Search for exclusive b→u semileptonic decays of B mesons
Date: 1993-01-01
Creator: A. Bean
J. Gronberg
R. Kutschke
S. Menary
R. J., Morrison
H. N. Nelson
J. D. Richman
H. Tajima
D. Schmidt
D. Sperka
M. S. Witherell
M. Procario
S. Yang
R. Ballest
M. Daoudi
W. T. Ford
D. R. Johnson
K. Lingel
M. Lohner
P. Rankin
J. G. Smith
J. P. Alexander
C. Bebek
K. Berkelman
D. Besson
T. E. Browder
D. G. Cassel
H. A. Cho
D. M. Coffman
P. S. Drell
R. Ehrlich
Access: Open access
- Using a sample of 935 000 BB̄ pairs collected with the CLEO-II detector at the Cornell Electron Storage Ring, we have obtained upper limits on the branching ratios for the b→ul-ν̄ processes B-→ωl- ν̄, B-→ρ0l-ν̄, and B̄0→ρ+l-ν̄. The combined result using the relationships among the widths for these three modes is B(B-→ρ0l-ν̄)<(1.6-2.7)×10-4 at 90% C.L., where the range of values is due to model dependence of the detection efficiencies. These measurements yield the limits Vub/Vcb<0.08-0.13. © 1993 The American Physical Society.
Differential neuropeptide modulation of premotor and motor neurons in the lobster cardiac ganglion
Date: 2020-10-01
Creator: Emily R. Oleisky
Meredith E. Stanhope
J. Joe Hull
Andrew E. Christie
Patsy S., Dickinson
Access: Open access
- The American lobster, Homarus americanus, cardiac neuromuscular system is controlled by the cardiac ganglion (CG), a central pattern generator consisting of four premotor and five motor neurons. Here, we show that the premotor and motor neurons can establish independent bursting patterns when decoupled by a physical ligature. We also show that mRNA encoding myosuppressin, a cardioactive neuropeptide, is produced within the CG. We thus asked whether myosuppressin modulates the decoupled premotor and motor neurons, and if so, how this modulation might underlie the role(s) that these neurons play in myosuppressin's effects on ganglionic output. Although myosuppressin exerted dose-dependent effects on burst frequency and duration in both premotor and motor neurons in the intact CG, its effects on the ligatured ganglion were more complex, with different effects and thresholds on the two types of neurons. These data suggest that the motor neurons are more important in determining the changes in frequency of the CG elicited by low concentrations of myosuppressin, whereas the premotor neurons have a greater impact on changes elicited in burst duration. A single putative myosuppressin receptor (MSR-I) was previously described from the Homarus nervous system. We identified four additional putative MSRs (MSR-II-V) and investigated their individual distributions in the CG premotor and motor neurons using RT-PCR. Transcripts for only three receptors (MSR-II-IV) were amplified from the CG. Potential differential distributions of the receptors were observed between the premotor and motor neurons; these differences may contribute to the distinct physiological responses of the two neuron types to myosuppressin. NEW & NOTEWORTHY Premotor and motor neurons of the Homarus americanus cardiac ganglion (CG) are normally electrically and chemically coupled, and generate rhythmic bursting that drives cardiac contractions; we show that they can establish independent bursting patterns when physically decoupled by a ligature. The neuropeptide myosuppressin modulates different aspects of the bursting pattern in these neuron types to determine the overall modulation of the intact CG. Differential distribution of myosuppressin receptors may underlie the observed responses to myosuppressin.
High Cryptic Diversity across the Global Range of the Migratory Planktonic Copepods Pleuromamma piseki and P. gracilis
Date: 2013-10-22
Creator: Kristin M.K. Halbert
Erica Goetze
David B. Carlon
Access: Open access
- Although holoplankton are ocean drifters and exhibit high dispersal potential, a number of studies on single species are finding highly divergent genetic clades. These cryptic species complexes are important to discover and describe, as identification of common marine species is fundamental to understanding ecosystem dynamics. Here we investigate the global diversity within Pleuromamma piseki and P. gracilis, two dominant members of the migratory zooplankton assemblage in subtropical and tropical waters worldwide. Using DNA sequence data from the mitochondrial gene cytochrome c oxidase subunit II (mtCOII) from 522 specimens collected across the Pacific, Atlantic and Indian Oceans, we discover twelve well-resolved genetically distinct clades in this species complex (Bayesian posterior probabilities >0.7; 6.3-17% genetic divergence between clades). The morphologically described species P. piseki and P. gracilis did not form monophyletic groups, rather they were distributed throughout the phylogeny and sometimes co-occurred within well-resolved clades: this result suggests that morphological characters currently used for taxonomic identification of P. gracilis and P. piseki may be inaccurate as indicators of species' boundaries. Cryptic clades within the species complex ranged from being common to rare, and from cosmopolitan to highly restricted in distribution across the global ocean. These novel lineages appear to be ecologically divergent, with distinct biogeographic distributions across varied pelagic habitats. We hypothesize that these mtDNA lineages are distinct species and suggest that resolving their systematic status is important, given the ecological significance of the genus Pleuromamma in subtropical-tropical waters worldwide. © 2013 Halbert et al.
A 60 yr record of atmospheric carbon monoxide reconstructed from Greenland firn air
Date: 2013-08-19
Creator: V. V. Petrenko
P. Martinerie
P. Novelli
D. M. Etheridge
I., Levin
Z. Wang
T. Blunier
J. Chappellaz
J. Kaiser
P. Lang
L. P. Steele
S. Hammer
J. Mak
R. L. Langenfelds
J. Schwander
J. P. Severinghaus
E. Witrant
G. Petron
M. O. Battle
G. Forster
W. T. Sturges
J. F. Lamarque
K. Steffen
J. W.C. White
Access: Open access
- We present the first reconstruction of the Northern Hemisphere (NH) high latitude atmospheric carbon monoxide (CO) mole fraction from Greenland firn air. Firn air samples were collected at three deep ice core sites in Greenland (NGRIP in 2001, Summit in 2006 and NEEM in 2008). CO records from the three sites agree well with each other as well as with recent atmospheric measurements, indicating that CO is well preserved in the firn at these sites. CO atmospheric history was reconstructed back to the year 1950 from the measurements using a combination of two forward models of gas transport in firn and an inverse model. The reconstructed history suggests that Arctic CO in 1950 was 140-150 nmol mol-1, which is higher than today's values. CO mole fractions rose by 10-15 nmol mol-1 from 1950 to the 1970s and peaked in the 1970s or early 1980s, followed by a ≈ 30 nmol mol-1 decline to today's levels. We compare the CO history with the atmospheric histories of methane, light hydrocarbons, molecular hydrogen, CO stable isotopes and hydroxyl radicals (OH), as well as with published CO emission inventories and results of a historical run from a chemistry-transport model. We find that the reconstructed Greenland CO history cannot be reconciled with available emission inventories unless unrealistically large changes in OH are assumed. We argue that the available CO emission inventories strongly underestimate historical NH emissions, and fail to capture the emission decline starting in the late 1970s, which was most likely due to reduced emissions from road transportation in North America and Europe. © Author(s) 2013.