Showing 771 - 780 of 2040 Items
Ocean primary production derived from satellite data: An evaluation with atmospheric oxygen measurements
Date: 1999-06-01
Creator: Yves Balkanski
Patrick Monfray
Mark Battle
Martin Heimann
Access: Open access
- Recently, very precise measurements have detected the seasonal variability in the atmospheric O2/N2 ratio at several sites in the northern and southern hemispheres. In this paper, we derive marine primary productivity (PP) from satellite ocean color data. To infer air-sea oxygen fluxes, a simple one-dimensional diagnostic model of ocean biology has been developed that depends on only two parameters: a time delay between organic production and oxidation (set to 2 weeks) and an export scale length (50 m). This model gives a global net community production of 4.3 mol C m-2 yr-1 in the euphotic zone and 3.2 mol C m-2 yr-1 in the mixed layer. This last value corresponds to a global f ratio (net community production (NCP)/PP) at the base of the mixed layer of 0.37. The air-sea fluxes derived from this model are then used at the base of a three-dimensional atmospheric model to compare the atmospheric seasonal cycle of O2/N2 at five sites: Cape Grim (40.6S, 144.6E), Baring Head (41.3S, 174.8E), Mauna Loa (19.5N,154.8W), La Jolla (32.9N, 117.3W), and Barrow (71.3N, 156.6W). The agreement between model and observations is very encouraging. We infer from the agreement that the seasonal variations in O2/N2 are largely controlled by the photosynthesis rate but also by the remineralization linked to the deepening and shoaling of the mixed layer. Lateral ventilation to high latitudes may also be an important factor controlling the amplitude of the seasonal cycle.
Identification of the determinants for the specific recognition of single-strand telomeric DNA by Cdc13
Date: 2006-01-24
Creator: Aimee M. Eldridge
Wayne A. Halsey
Deborah S. Wuttke
Access: Open access
- The single-strand overhang present at telomeres plays a critical role in mediating both the capping and telomerase regulation functions of telomeres. The telomere end-binding proteins, Cdc13 in Saccharomyces cerevisiae, Pot1 in higher eukaryotes, and TEBP in the ciliated protozoan Oxytricha nova, exhibit sequence-specific binding to their respective single-strand overhangs. S. cerevisiae telomeres are composed of a heterogeneous mixture of GT-rich telomeric sequence, unlike in higher eukaryotes which have a simple repeat that is maintained with high fidelity. In yeast, the telomeric overhang is recognized by the essential protein Cdc13, which coordinates end-capping and telomerase activities at the telomere. The Cdc13 DNA-binding domain (Cdc13-DBD) binds these telomere sequences with high affinity (3 pM) and sequence specificity. To better understand the basis for this remarkable recognition, we have investigated the binding of the Cdc13-DBD to a series of altered DNA substrates. Although an 11-mer of GT-rich sequence is required for full binding affinity, only three of these 11 bases are recognized with high specificity. This specificity differs from that observed in the other known telomere end-binding proteins, but is well suited to the specific role of Cdc13 at yeast telomeres. These studies expand our understanding of telomere recognition by the Cdc13-DBD and of the unique molecular recognition properties of ssDNA binding. © 2006 American Chemical Society.
Production and decay of D1 (2420)0 and D2* (2460)0
Date: 1994-06-30
Creator: P. Avery
A. Freyberger
J. Rodriguez
R. Stephens
S., Yang
J. Yelton
D. Cinabro
S. Henderson
T. Liu
M. Saulnier
R. Wilson
H. Yamamoto
T. Bergfeld
B. I. Eisenstein
G. Gollin
B. Ong
M. Palmer
M. Selen
J. J. Thaler
K. W. Edwards
M. Ogg
B. Spaan
A. Bellerive
D. I. Britton
E. R.F. Hyatt
D. B. MacFarlane
P. M. Patel
A. J. Sadoff
R. Ammar
S. Ball
P. Baringer
Access: Open access
- We have investigated D+ π- and D*+ π- final states and observed the two established L = 1 charmed mesons, the D1 (2420)0 with mass 2421-2-2+1+2 MeV/c2 and width 20-5-3+6+3 MeV/c2 and the D2* (2460)0 with mass 2465 ± 3 ± 3 MeV/c2 and width 28-7-6+8+6 MeV/c2. Properties of these final states, including their decay angular distributions and spin-parity assignments, have been studied. We identify these two mesons as the jlight = 3 2 doublet predicted by HQET. We also obtain constraints on Γs/ (Γs + ΓD) as a function of the cosine of the relative phase of the two amplitudes in the D1 (2420)0 decay. © 1994.
A structural role for arginine in proteins: Multiple hydrogen bonds to backbone carbonyl oxygens
Date: 1994-01-01
Creator: C. L. Borders
John A. Broadwater
Paula A. Bekeny
Johanna E. Salmon
Ann S., Lee
Aimee M. Eldridge
Virginia B. Pett
Access: Open access
- We propose that arginine side chains often play a previously unappreciated general structural role in the maintenance of tertiary structure in proteins, wherein the positively charged guanidinium group forms multiple hydrogen bonds to backbone carbonyl oxygens. Using as a criterion for a “structural” arginine one that forms 4 or more hydrogen bonds to 3 or more backbone carbonyl oxygens, we have used molecular graphics to locate arginines of interest in 4 proteins: Arg 180 in Thermus thermophilus manganese superoxide dismutase, Arg 254 in human carbonic anhydrase II, Arg 31 in Streptomyces rubiginosus xylose isomerase, and Arg 313 in Rhodospirillum rubrum ribulose‐1,5‐bisphosphate carboxylase/oxygenase. Arg 180 helps to mold the active site channel of superoxide dismutase, whereas in each of the other enzymes the structural arginine is buried in the “mantle” (i.e., inside, but near the surface) of the protein interior well removed from the active site, where it makes 5 hydrogen bonds to 4 backbone carbonyl oxygens. Using a more relaxed criterion of 3 or more hydrogen bonds to 2 or more backbone carbonyl oxygens, arginines that play a potentially important structural role were found in yeast enolase, Bacillus stearothermophilus glyceraldehyde‐3‐phosphate dehydrogenase, bacteriophage T4 and human lysozymes, Enteromorpha prolifera plastocyanin, HIV‐1 protease, Trypanosoma brucei brucei and yeast triosephosphate isomerases, and Escherichia coli trp aporepressor (but not trp repressor or the trp repressor/operator complex). In addition to helping form the active site funnel in superoxide dismutase, the structural arginines found in this study play such diverse roles as stapling together 3 strands of backbone from different regions of the primary sequence, and tying α‐helix to α‐helix, βturn to β‐turn, and subunit to subunit. Copyright © 1994 The Protein Society
A structural role for arginine in proteins: Multiple hydrogen bonds to backbone carbonyl oxygens
Date: 1994-01-01
Creator: C. L. Borders
John A. Broadwater
Paula A. Bekeny
Johanna E. Salmon
Ann S., Lee
Aimee M. Eldridge
Virginia B. Pett
Access: Open access
- We propose that arginine side chains often play a previously unappreciated general structural role in the maintenance of tertiary structure in proteins, wherein the positively charged guanidinium group forms multiple hydrogen bonds to backbone carbonyl oxygens. Using as a criterion for a “structural” arginine one that forms 4 or more hydrogen bonds to 3 or more backbone carbonyl oxygens, we have used molecular graphics to locate arginines of interest in 4 proteins: Arg 180 in Thermus thermophilus manganese superoxide dismutase, Arg 254 in human carbonic anhydrase II, Arg 31 in Streptomyces rubiginosus xylose isomerase, and Arg 313 in Rhodospirillum rubrum ribulose‐1,5‐bisphosphate carboxylase/oxygenase. Arg 180 helps to mold the active site channel of superoxide dismutase, whereas in each of the other enzymes the structural arginine is buried in the “mantle” (i.e., inside, but near the surface) of the protein interior well removed from the active site, where it makes 5 hydrogen bonds to 4 backbone carbonyl oxygens. Using a more relaxed criterion of 3 or more hydrogen bonds to 2 or more backbone carbonyl oxygens, arginines that play a potentially important structural role were found in yeast enolase, Bacillus stearothermophilus glyceraldehyde‐3‐phosphate dehydrogenase, bacteriophage T4 and human lysozymes, Enteromorpha prolifera plastocyanin, HIV‐1 protease, Trypanosoma brucei brucei and yeast triosephosphate isomerases, and Escherichia coli trp aporepressor (but not trp repressor or the trp repressor/operator complex). In addition to helping form the active site funnel in superoxide dismutase, the structural arginines found in this study play such diverse roles as stapling together 3 strands of backbone from different regions of the primary sequence, and tying α‐helix to α‐helix, βturn to β‐turn, and subunit to subunit. Copyright © 1994 The Protein Society
Multi-colony calibrations of coral Ba/Ca with a contemporaneous in situ seawater barium record
Date: 2016-04-15
Creator: Michèle LaVigne
Andréa G. Grottoli
James E. Palardy
Robert M. Sherrell
Access: Open access
- The coral skeleton barium to calcium ratio (Ba/Ca ), a proxy for seawater barium concentrations (Ba ), has been interpreted as a tracer of upwelling based on the characteristic "nutrient like" depth profile of Ba . However, in some tropical regions, such as the Gulf of Panamá, substantial influence of terrestrial runoff inputs and differences between the vertical distribution of Ba and that of the major nutrients (nitrate and phosphate) in the upper water column can complicate the interpretation of Ba/Ca as an upwelled nutrient proxy. In the Gulf of Panamá, contemporaneous Ba/Ca records from multiple colonies of Porites lobata, Pavona gigantea, and Pavona clavus corals record a nearly twofold change in surface water Ba as a 20-70% increase in skeletal Ba/Ca with excellent correlation among Ba/Ca records from co-located colonies (r = 0.86-0.99). These results provide, for the first time, an absolute calibration of the coral Ba proxy with a contemporaneous Ba record. Compiling the Ba/Ca records from three co-located colonies of each species into taxon-specific composite regressions reveals strong statistically significant correlations with the Ba time-series record (p < 0.001). Differences among taxa in regression slope, y-intercept, and average distribution coefficient, as well as a demonstration of the application of the P. clavus calibration to a previously published Ba/Ca record, emphasize the necessity of using taxon-specific calibrations to reconstruct changes in Ba with accuracy. These results support the application of Ba/Ca to reconstruct past changes in absolute Ba concentrations, adding an important tool to the collection of geochemical proxies for reconstructing surface ocean biogeochemical processes in the past. coral SW SW SW coral coral SW SW coral SW coral SW coral SW
Unidirectional Transition Waves in Bistable Lattices
Date: 2016-06-13
Creator: Neel Nadkarni
Andres F. Arrieta
Christopher Chong
Dennis M. Kochmann
Chiara, Daraio
Access: Open access
- We present a model system for strongly nonlinear transition waves generated in a periodic lattice of bistable members connected by magnetic links. The asymmetry of the on-site energy wells created by the bistable members produces a mechanical diode that supports only unidirectional transition wave propagation with constant wave velocity. We theoretically justify the cause of the unidirectionality of the transition wave and confirm these predictions by experiments and simulations. We further identify how the wave velocity and profile are uniquely linked to the double-well energy landscape, which serves as a blueprint for transition wave control.
Associations Between Mode of Birth and Neuropsychological Development in Children Aged 4 Years: Results from a Birth Cohort Study
Date: 2021-12-01
Creator: Lea Takács
Samuel P. Putnam
Catherine Monk
Hannah G. Dahlen
Charlene, Thornton
František Bartoš
Anastasia Topalidou
Lilian L. Peters
Access: Open access
- The aim of this prospective longitudinal study was to examine the association between Cesarean section (CS) and child development and behavior. The sample consisted of 256 children who were born at term without serious perinatal pathologies. Their development and behavior was assessed at the age of four using Ages and Stages Questionnaire (ASQ-3), Children’s Behavior Questionnaire and Strength and Difficulties Questionnaire. Multivariate linear regression analyses were conducted to assess the association between CS and child outcomes. CS was associated with better scores in the Problem Solving domain of the ASQ in the whole sample. After stratifying by child sex, the positive association between CS and the Problem Solving domain was significant in boys, while no association was found in girls. Girls were rated less optimally in the Gross Motor domain of the ASQ when born via CS. Mode of birth was not associated with behavioral outcomes.
Nonlinear vibrational-state excitation and piezoelectric energy conversion in harmonically driven granular chains
Date: 2016-05-05
Creator: C. Chong
E. Kim
E. G. Charalampidis
H. Kim
F., Li
P. G. Kevrekidis
Access: Open access
- This article explores the excitation of different vibrational states in a spatially extended dynamical system through theory and experiment. As a prototypical example, we consider a one-dimensional packing of spherical particles (a so-called granular chain) that is subject to harmonic boundary excitation. The combination of the multimodal nature of the system and the strong coupling between the particles due to the nonlinear Hertzian contact force leads to broad regions in frequency where different vibrational states are possible. In certain parametric regions, we demonstrate that the nonlinear Schrödinger equation predicts the corresponding modes fairly well. The electromechanical model we apply predicts accurately the conversion from the obtained mechanical energy to the electrical energy observed in experiments.
Where to put things? Spatial land management to sustain biodiversity and economic returns
Date: 2008-06-01
Creator: Stephen Polasky
Erik Nelson
Jeff Camm
Blair Csuti
Paul, Fackler
Eric Lonsdorf
Claire Montgomery
Denis White
Jeff Arthur
Access: Open access
- Expanding human population and economic growth have led to large-scale conversion of natural habitat to human-dominated landscapes with consequent large-scale declines in biodiversity. Conserving biodiversity, while at the same time meeting expanding human needs, is an issue of utmost importance. In this paper we develop a spatially explicit landscape-level model for analyzing the biological and economic consequences of alternative land-use patterns. The spatially explicit biological model incorporates habitat preferences, area requirements and dispersal ability between habitat patches for terrestrial vertebrate species to predict the likely number of species that will be sustained on the landscape. The spatially explicit economic model incorporates site characteristics and location to predict economic returns for a variety of potential land uses. We apply the model to search for efficient land-use patterns that maximize biodiversity conservation objectives for given levels of economic returns, and vice versa. We apply the model to the Willamette Basin, Oregon, USA. By thinking carefully about the arrangement of activities, we find land-use patterns that sustain high levels of biodiversity and economic returns. Compared to the 1990 land-use pattern, we show that both biodiversity conservation and the value of economic activity could be increased substantially. © 2008 Elsevier Ltd.