Showing 751 - 760 of 2040 Items

Mercury in the snow and firn at Summit Station, Central Greenland, and implications for the study of past atmospheric mercury levels

Date: 2008-06-30

Creator: X. Faïn

C. P. Ferrari

A. Dommergue

M. Albert

M., Battle

L. Arnaud

J. M. Barnola

W. Cairns

C. Barbante

C. Boutron

Access: Open access

Gaseous Elemental Mercury (Hg° or GEM) was investigated at Summit Station, Greenland, in the interstitial air extracted from the perennial snowpack (firn) at depths ranging from the surface to 30 m, during summer 2005 and spring 2006. Photolytic production and destruction of Hg° were observed close to the snow surface during summer 2005 and spring 2006, and we observed dark oxidation of GEM up to 270 cm depth in June 2006. Photochemical transformation of gaseous elemental mercury resulted in diel variations in the concentrations of this gas in the near-surface interstitial air, but destruction of Hg° was predominant in June, and production was the main process in July. This seasonal evolution of the chemical mechanisms involving gaseous elemental mercury produces a signal that propagates downward through the firn air, but is unobservably small below 15 m in depth. As a consequence, multi-annual averaged records of GEM concentration should be well preserved in deep firn air at depths below 15 m, and available for the reconstruction of the past atmospheric history of GEM over the last decades.


Localization of DNA sequences promoting RNA polymerase I activity in Drosophila

Date: 1983-01-01

Creator: B. D. Kohorn

P. M.M. Rae

Access: Open access



On the nature of eγ and non-vanishing of derivatives of L-series at s=1/2

Date: 2014-04-30

Creator: M. Ram Murty

Naomi Tanabe

Access: Open access

In 2011, M.R. Murty and V.K. Murty [10] proved that if L(s, χD) is the Dirichlet L-series attached a quadratic character χD, and L'(1, χD)=0, then eγ is transcendental. This paper investigates such phenomena in wider collections of L-functions, with a special emphasis on Artin L-functions. Instead of s=1, we consider s=1/2. More precisely, we prove thatexp (L'(1/2,χ)L(1/2,χ)-αγ) is transcendental with some rational number α. In particular, if we have L(1/2, χ)≠0 and L'(1/2, χ)=0 for some Artin L-series, we deduce the transcendence of eγ.


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.