Showing 361 - 370 of 733 Items
Accurate transcription of truncated ribosomal DNA templates in a Drosophila cell-free system
Date: 1982-01-01
Creator: B. D. Kohorn, P. M.M. Rae
Access: Open access
- An extract of Drosophila melanogaster Kc cells is shown to give specific and accurate transcription of truncated segments of cloned D. melanogaster ribosomal DNA (rDNA). When clones are digested with restriction enzymes so that the initiation site is flanked by 0.3 kilobase (kb) of nontranscribed spacer and >0.4 kb of external transcribed spacer, RNA polymerase I activity in the extract parallels in vivo rRNA synthesis in selection of the coding strand of template and the site of transcription initiation. When >0.3 kb of the nontranscribed spacer is contiguous with transcribed spacer, in vitro initiations evidently also occur in repeated sequences adjacent to the site of in vivo initiation; when ≤0.4 kb of the external transcribed spacer is present in a segment, expected transcripts are heterogeneous in length or not detectable. Transcription in the cell-free system requires the specific addition of D. melanogaster rDNA: neither D. virilis rDNA, vector plasmid, nor clones of D. melanogaster genes that are transcribed in vivo by RNA polymerases II and III serve as templates in the system. Drosophila rDNA units that have an interruption in the 28S rRNA coding region are not transcribed in vivo, but restriction digests of a recombinant phage DNA that contains such a unit are active as template for in vitro rDNA transcription.
Transient phenomena in ecology
Date: 2018-09-07
Creator: Alan Hastings, Karen C. Abbott, Kim Cuddington, Tessa Francis, Gabriel, Gellner, Ying Cheng Lai
Access: Open access
- The importance of transient dynamics in ecological systems and in the models that describe them has become increasingly recognized. However, previous work has typically treated each instance of these dynamics separately. We review both empirical examples and model systems, and outline a classification of transient dynamics based on ideas and concepts from dynamical systems theory. This classification provides ways to understand the likelihood of transients for particular systems, and to guide investigations to determine the timing of sudden switches in dynamics and other characteristics of transients. Implications for both management and underlying ecological theories emerge.
Atmospheric O2/N2 changes, 1993-2002: Implications for the partitioning of fossil fuel CO2 sequestration
Date: 2005-12-01
Creator: Michael L. Bender, David T. Ho, Melissa B. Hendricks, Robert Mika, Mark O., Battle, Pieter P. Tans, Thomas J. Conway, Blake Sturtevant, Nicolas Cassar
Access: Open access
- Improvements made to an established mass spectrometric method for measuring changes in atmospheric O2/N2 are described. With the improvements in sample handling and analysis, sample throughput and analytical precision have both increased. Aliquots from duplicate flasks are repeatedly measured over a period of 2 weeks, with an overall standard error in each flask of 3-4 per meg, corresponding to 0.6-0.8 ppm O2 in air. Records of changes in O2/N2 from six global sampling stations (Barrow, American Samoa, Cape Grim, Amsterdam Island, Macquarie Island, and Syowa Station) are presented. Combined with measurements Of CO2 from the same sample flasks, land and ocean carbon uptake were calculated from the three sampling stations with the longest records (Barrow, Samoa, and Cape Grim). From 1994-2002, We find the average CO2 uptake by the ocean and the land biosphere was 1.7 ± 0.5 and 1.0 ± 0.6 GtC yr -1 respectively; these numbers include a correction of 0.3 Gt C yr-l due to secular outgassing of ocean O2. Interannual variability calculated from these data shows a strong land carbon source associated with the 1997-1998 El Niño event, supporting many previous studies indicating that high atmospheric growth rates observed during most El Niño events reflect diminished land uptake. Calculations of interannual variability in land and ocean uptake are probably confounded by non-zero annual air sea fluxes of O2. The origin of these fluxes is not yet understood. Copyright 2005 by the American Geophysical Union.
Environmental issues in russia
Date: 2008-12-01
Creator: Laura A. Henry, Vladimir Douhovnikoff
Access: Open access
- This review examines the literature available on the state of the environment and environmental protection in the Russian Federation. As the largest country on Earth, rich in natural resources and biodiversity, Russia's problems and policies have global consequences. Environmental quality and management are influenced by the legacy of Soviet economic planning and authoritarian governance, as well as by Russia's post-Soviet economic recession and current strategies of economic development. Russia achieved a reduction in some pollutants owing to the collapse of industrial production in the 1990s, but many environmental indicators suggest growing degradation. Russia has signed on to a number of international environmental agreements, but its record on implementation is mixed, and it discourages environmental activism. Scholarship on the Russian environment is a limited, but growing, field, constrained by challenges of data availability, yet it offers great potential for testing scientific and social scientific hypotheses. ©2008 by Annual Reviews.
Is variation in susceptibility to Phytophthora ramorum correlated with population genetic structure in coast live oak (Quercus agrifolia)?
Date: 2005-01-01
Creator: Richard S. Dodd, Daniel Hüberli, Vlad Douhovnikoff, Tamar Y. Harnik, Zara, Afzal-Rafii, Matteo Garbelotto
Access: Open access
- California coastal woodlands are suffering severe disease and mortality as a result of infection from Phytophthora ramorum. Quercus agrifolia is one of the major woodland species at risk. This study investigated within- and among-population variation in host susceptibility to inoculation with P. ramorum and compared this with population genetic structure using molecular markers. Susceptibility was assessed using a branch-cutting inoculation test. Trees were selected from seven natural populations in California. Amplified fragment length polymorphism molecular markers were analysed for all trees used in the trials. Lesion sizes varied quantitatively among individuals within populations, with up to an eightfold difference. There was little support for population differences in susceptibility. Molecular structure also showed a strong within-population, and weaker among-population, pattern of variation. Our data suggest that susceptibility of Q. agrifolia to P. ramorum is variable and is under the control of several gene loci. This variation exists within populations, so that less susceptible local genotypes may provide the gene pool for regeneration of woodlands where mortality is high. © New Phytologist (2004).
Measurement of the cross section for γγ→pp̄
Date: 1994-01-01
Creator: 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, G. Eigen, J. S. Miller, C. O'Grady, J. Urheim, A. J. Weinstein, D. Acosta, M. Athanas
Access: Open access
- A measurement of the cross section for γγ→pp̄ is performed at two-photon center-of-mass energies between 2.00 and 3.25 GeV. These results are obtained using e+e-→e+e-pp̄ events selected from 1.31 fb-1 of data taken with the CLEO II detector. The measured cross section is in reasonable agreement with previous measurements and is in excellent agreement with recent calculations based on a diquark model. However, leading order QCD calculations performed using the Brodsky-Lepage formalism are well below the measured cross section. © 1994 The American Physical Society.
Sexual reproduction is more prevalent in continental landscapes in the expanding arctic shrub, Salix glauca
Date: 2019-12-01
Creator: David A. Watts, Vladimir Douhovnikoff, Eric Post
Access: Open access
- The recent expansion of arctic deciduous shrubs has been well documented across a range of habitats, but the phenomenon is not universal. Their spread is often associated with increases in temperature and other abiotic factors, while variation in habitat moisture and herbivory can mediate the location and rate of this rise in abundance. Much less is known about the mode of increase of arctic shrubs. For one such shrub, Salix glauca, we used microsatellite markers to assess the prevalence of clonal growth (i.e. vegetative spread) and sexual reproduction (i.e. recruitment from seed) at sites with maritime and continental climates and differing in the density of large herbivores. We sampled individuals in plots reflecting the spatial scale of expansion in locations where S. glauca recently increased in abundance. The 400 samples collected across the four sites comprised 310 genotypes. Though evidence of sexual recruitment was common across all sites, coastal sites contained both more and larger clonal genotypes. While we expected soil conditions would be influential, the factors that best predicted the likelihood of clonality, genet size and vascular plant cover, suggest the light environment is of primary importance. Furthermore, in spite of the large distances between sites, there was no suggestion of genetic differentiation into distinct populations. These results indicate that differences in climate and herbivory can influence not only where and how extensively deciduous shrubs spread, but how they are likely to do so. We suggest future research integrating how mode of increase is associated with the rate of spread will advance projections of change in arctic ecosystems.
Study of the five-charged-pion decay of the τ lepton
Date: 1994-01-01
Creator: D. Gibaut, 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, M. Athanas, 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, M. Procario, R. Balest, K. Cho
Access: Open access
- The branching fractions for the five-charged-particle decays of the τ lepton have been measured in e+e- annihilations using the CLEO II detector at the Cornell Electron Storage Ring. Assuming all charged particles to be pions, the results are B(3π-2π+0 neutrals ντ)=(0.097±0. 005±0.011)%, B(3π-2π+ντ)=(0.077±0.005 ±0.009)%, B(3π-2π+π0ντ)=(0.019±0.004±0.004) %, and B(3π-2π+2π0ντ)<0.011% at the 90% C.L. B(3π-2π-π0ντ) is measured for the first time by exclusive π0 reconstruction. The results are compared with the predictions from the partially conserved-axial-current and conserved-vector-current hypotheses assuming isospin invariance. © 1994 The American Physical Society.
Observation of inclusive B decays to the charmed baryons c++ and c0
Date: 1994-01-01
Creator: M. Procario, R. Balest, K. Cho, M. Daoudi, 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, H. A. Cho, D. M. Coffman, P. S. Drell, R. Ehrlich, R. S. Galik, M. Garcia-Sciveres, B. Geiser, B. Gittelman, S. W. Gray, D. L. Hartill, B. K. Heltsley, C. D. Jones, S. L. Jones, J. Kandaswamy, N. Katayama
Access: Open access
- Using data collected in the region of the γ(4S) resonance with the CLEO II detector operating at the Cornell Electron Storage Ring, we report on evidence for the production of ++ and c0 baryons in B decays, with c→Λc+π. This observation is based on 77±19 c++ and 76±21 c0 candidates from B decays. We find the product branching fractions B(B̄→cX)B(Λc+→pK-π+) for c=c++, c0, and c+ to be (2.1 ± 0.8 ± 0.7) × 10-4, (2.3 ± 0.8 ± 0.7) × 10-4, and less than 4.8 × 10-4 at 90% confidence level, respectively. A study of the c++ and c0 momentum spectra indicates that B decays to two-body final states with c are suppressed. © 1994 The American Physical Society.
A revised 1000 year atmospheric δ13 C-CO2 record from Law Dome and South Pole, Antarctica
Date: 2013-08-16
Creator: M. Rubino, D. M. Etheridge, C. M. Trudinger, C. E. Allison, M. O., Battle, R. L. Langenfelds, L. P. Steele, M. Curran, M. Bender, J. W.C. White, T. M. Jenk, T. Blunier, R. J. Francey
Access: Open access
- We present new measurements of δ13C of CO2 extracted from a high-resolution ice core from Law Dome (East Antarctica), together with firn measurements performed at Law Dome and South Pole, covering the last 150 years. Our analysis is motivated by the need to better understand the role and feedback of the carbon (C) cycle in climate change, by advances in measurement methods, and by apparent anomalies when comparing ice core and firn air δ13C records from Law Dome and South Pole. We demonstrate improved consistency between Law Dome ice, South Pole firn, and the Cape Grim (Tasmania) atmospheric δ13C data, providing evidence that our new record reliably extends direct atmospheric measurements back in time. We also show a revised version of early δ13C measurements covering the last 1000 years, with a mean preindustrial level of -6.50‰. Finally, we use a Kalman Filter Double Deconvolution to infer net natural CO2 fluxes between atmosphere, ocean, and land, which cause small δ13C deviations from the predominant anthropogenically induced δ13C decrease. The main features found from the previous δ13C record are confirmed, including the ocean as the dominant cause for the 1940 A.D. CO2 leveling. Our new record provides a solid basis for future investigation of the causes of decadal to centennial variations of the preindustrial atmospheric CO2 concentration. Those causes are of potential significance for predicting future CO2 levels and when attempting atmospheric verification of recent and future global carbon emission mitigation measures through Coupled Climate Carbon Cycle Models. Key Points New and revised, firn and ice δ13C-CO2 measurements from Antarctica Improve consistency between ice and firn δ13C-CO2 measurements Net natural CO2 fluxes between atmosphere, ocean and land inferred ©2013. American Geophysical Union. All Rights Reserved.