Showing 651 - 700 of 733 Items

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.

Date: 1993-01-01

Creator: S. G. Naculich, C. P. Yuan

Access: Open access

If the electroweak symmetry-breaking sector becomes strongly interacting at high energies, it can be probed through longitudinal W scattering. We present a model with many inelastic channels in the WLWL scattering process, corresponding to the production of heavy fermion pairs. These heavy fermions affect the elastic scattering of WL's by propagating in loops, greatly reducing the amplitudes in some charge channels. We conclude that the symmetry-breaking sector cannot be fully explored by using, for example, the WL±WL± mode alone, even when no resonance is present; all WLWL→WLWL scattering modes must be measured. © 1993 The American Physical Society.

Date: 2010-01-01

Creator: Johannes M. Henn, Stephen G. Naculich, Howard J. Schnitzer, Marcus Spradlin

Access: Open access

We compute the three-loop contribution to the N = 4 supersymmetric Yang- Mills planar four-gluon amplitude using the recently-proposed Higgs IR regulator of Alday, Henn, Plefka, and Schuster. In particular, we test the proposed exponential ansatz for the four-gluon amplitude that is the analog of the BDS ansatz in dimensional regularization. By evaluating our results at a number of kinematic points, and also in several kinematic limits, we establish the validity of this ansatz at the three-loop level. We also examine the Regge limit of the planar four-gluon amplitude using several different IR regulators: dimensional regularization, Higgs regularization, and a cutoff regularization. In the latter two schemes, it is shown that the leading logarithmic (LL) behavior of the amplitudes, and therefore the lowest-order approximation to the gluon Regge trajectory, can be correctly obtained from the ladder approximation of the sum of diagrams. In dimensional regularization, on the other hand, there is no single dominant set of diagrams in the LL approximation. We also compute the NLL and NNLL behavior of the L-loop ladder diagram using Higgs regularization. © SISSA 2010.

Date: 1992-01-01

Creator: D. Bortoletto, D. N. Brown, J. Dominick, R. L. Mcilwain, T., Miao, D. H. Miller, M. Modesitt, S. F. Schaffner, E. I. Shibata, I. P.J. Shipsey, M. Battle, J. Ernst, H. Kroha, S. Roberts, K. Sparks, E. H. Thorndike, C. H. Wang, S. Sanghera, T. Skwarnicki, R. Stroynowski, M. Artuso, M. Goldberg, N. Horwitz, R. Kennett, G. C. Moneti, F. Muheim, S. Playfer, Y. Rozen, P. Rubin, S. Stone, M. Thulasidas

Access: Open access

Using the decay modes, D*+→D+π0 and D*0→D0π0, we have measured the D*+-D+ and D*0-D0 mass differences to be 140±0.08±0.06 and 142.12±0.05±0.05 MeV, respectively. Combining these measurements with the Particle Data Group average for the D*+-D0 mass difference, we obtain isospin mass splittings for D*+-Dusp*0 and D+-D0 of 3.32±0.08±0.05 and 4.80±0.10 ±0.06 MeV. We discuss the implications of these measurements for models of isospin mass differences and model-dependent estimates of fD. © 1992 The American Physical Society.

Date: 1992-10-29

Creator: S. G. Naculich, C. P. Yuan

Access: Open access

It has been argued that if light Higgs bosons do not exist then the self-interactions of W's become strong in the TeV region and can be observed in longitudinal WW scattering. We present a model with many inelastic channels in the WW scattering process, corresponding to the creation of heavy fermion pairs. The presence of these heavy fermions affects the elastic scattering of W's by propagating in loops, greatly reducing the amplitudes in some charge channels. Consequently, the symmetry-breaking sector cannot be fully explored by using, for example, the W+W+ mode alone; all WW→WW scattering modes must be measured. © 1992.

Date: 2012-01-01

Creator: Alexander C. Edison, Stephen G. Naculich

Access: Open access

Color-ordered amplitudes for the scattering of n particles in the adjoint representation of SU(N) gauge theory satisfy constraints that arise from group theory alone. These constraints break into subsets associated with irreducible representations of the symmetric group Sn, which allows them to be presented in a compact and natural way. Using an iterative approach, we derive the constraints for six-point amplitudes at all loop orders, extending earlier results for n = 4 and n = 5. We then decompose the four-, five-, and six-point group-theory constraints into their irreducible Sn subspaces. We comment briefly on higher-point two-loop amplitudes. © SISSA 2012.

Date: 2019-07-10

Creator: Mark O. Battle, J. William Munger, Margaret Conley, Eric Sofen, Rebecca, Perry, Ryan Hart, Zane Davis, Jacob Scheckman, Jayme Woogerd, Karina Graeter, Samuel Seekins, Sasha David, John Carpenter

Access: Open access

Measurements of atmospheric O2 have been used to quantify large-scale fluxes of carbon between the oceans, atmosphere and land since 1992 (Keeling and Shertz, 1992). With time, datasets have grown and estimates of fluxes have become more precise, but a key uncertainty in these calculations is the exchange ratio of O2 and CO2 associated with the net land carbon sink (B). We present measurements of atmospheric O2 and CO2 collected over a 6-year period from a mixed deciduous forest in central Massachusetts, USA (42.537 N, 72.171 W). Using a differential fuel-cellbased instrument for O2 and a nondispersive infrared analyzer for CO2, we analyzed airstreams collected within and 5m above the forest canopy. Averaged over the entire period of record, we find these two species covary with a slope of -1:081±0:007 mol of O2 per mole of CO2 (the mean and standard error of 6 h periods). If we limit the data to values collected on summer days within the canopy, the slope is -1:03±0:01. These are the conditions in which biotic influences are most likely to dominate. This result is significantly different from the value of -1.1 widely used in O2-based calculations of the global carbon budget, suggesting the need for a deeper understanding of the exchange ratios of the various fluxes and pools comprising the net sink.

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.

Date: 2015-09-26

Creator: Stephen G. Naculich

Access: Open access

Abstract: In the formulation of Cachazo, He, and Yuan, tree-level amplitudes for massless particles in gauge theory and gravity can be expressed as rational functions of the Lorentz invariants ka · kb, ϵa · kb, and ϵa · ϵb, valid in any number of spacetime dimensions. We use dimensional reduction of higher-dimensional amplitudes of particles with internal momentum κ to obtain amplitudes for massive particles in lower dimensions. In the case of gauge theory, we argue that these massive amplitudes belong to a theory in which the gauge symmetry is spontaneously broken by an adjoint Higgs field. Consequently, we show that tree-level n-point amplitudes containing massive vector and scalar bosons in this theory can be obtained by simply replacing ka · kb with ka · kb − κaκb in the corresponding massless amplitudes, where the masses of the particles are given by |κa|.

Date: 2011-11-21

Creator: Stephen G. Naculich, Howard J. Schnitzer

Access: Open access

We derive a linear relation between the one-loop five-point amplitude of N = 8 supergravity and the one-loop five-point subleading-color amplitudes of N = 4 supersymmetric Yang-Mills theory. © 2011 SISSA.

Date: 2008-05-01

Creator: Stephen G. Naculich, Howard J. Schnitzer

Access: Open access

It is shown that the four-gluon scattering amplitude for N = 4 supersymmetric Yang-Mills theory in the planar limit can be written, in both the weak- and strong-coupling limits, as a reggeized amplitude, with a parent trajectory and an infinite number of daughter trajectories. This result is not evident a priori, and relies crucially on the fact that the leading IR-divergence and the finite log2 (s / t)-dependent piece of the amplitude are characterized by the same function for all values of the coupling, as conjectured by Bern, Dixon, and Smirnov, and proved by Alday and Maldacena in the strong-coupling limit. We use the Alday-Maldacena result to determine the exact strong-coupling Regge trajectory. © 2007 Elsevier B.V. All rights reserved.

Date: 1998-11-16

Creator: Stephen G. Naculich, Henric Rhedin, Howard J. Schnitzer

Access: Open access

One-instanton predictions are obtained from the Seiberg-Witten curve derived from M-theory by Landsteiner and Lopez for the Coulomb branch of N = 2 supersymmetric SU(N) gauge theory with a matter hypermultiplet in the antisymmetric representation. Since this cubic curve describes a Riemann surface that is non-hyperelliptic, a systematic perturbation expansion about a hyperelliptic curve is developed, with a comparable expansion for the Seiberg-Witten differential. Calculation of the period integrals of the SW differential by the method of residues of D'Hoker, Krichever, and Phong enables us to compute the prepotential explicitly to one-instanton order. It is shown that the one-instanton predictions for SU(2), SU(3), and SU(4) agree with previously available results. For SU(N), N ≥ 5, our analysis provides explicit predictions of a curve derived from M-theory at the one-instanton level in field theory. © 1998 Elsevier Science B.V.

Date: 1994-01-01

Creator: M. Battle, J. Ernst, Y. Kwon, S. Roberts, E. H., Thorndike, C. H. Wang, 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. Muheim, S. Playfer, Y. Rozen, S. Stone, M. Thulasidas, G. Vasseur, G. Zhu, J. Bartelt

Access: Open access

Branching ratios for the dominant Cabibbo-suppressed decays of the τ lepton have been measured by CLEO II in e+e- annihilation at the Cornell Electron Storage Ring (s∼10.6 GeV) using kaons with momenta below 0.7 GeV/c. The inclusive branching ratio into one charged kaon is (1.60 ± 0.12 ± 0.19)%. For the exclusive decays, B(τ-→K-ντ)=(0.66±0.07±0.09)%, B(τ-→K-π0ντ)=(0.51±0.10±0.07)%, and, based on three events, B(τ-→K-2π0ντ)<0.3% at the 90% confidence level. These represent significant improvements over previous results. B(τ-→K-π0ντ) is measured for the first time with exclusive π0 reconstruction. © 1994 The American Physical Society.

Date: 2006-03-28

Creator: Danielle H. Dube, Jennifer A. Prescher, Chi M. Quang, Carolyn R. Bertozzi

Access: Open access

Changes in O-linked protein glycosylation are known to correlate with disease states but are difficult to monitor in a physiological setting because of a lack of experimental tools. Here, we report a technique for rapid profiling of O-linked glycoproteins in living animals by metabolic labeling with N-azidoacetylgalactosamine (GalNAz) followed by Staudinger ligation with phosphine probes. After injection of mice with a peracetylated form of GalNAz, azide-labeled glycoproteins were observed in a variety of tissues, including liver, kidney, and heart, in serum, and on isolated splenocytes. B cell glycoproteins were robustly labeled with GalNAz but T cell glycoproteins were not, suggesting fundamental differences in glycosylation machinery or metabolism. Furthermore, GalNAz-labeled B cells could be selectively targeted with a phosphine probe by Staudinger ligation within the living animal. Metabolic labeling with GalNAz followed by Staudinger ligation provides a means for proteomic analysis of this posttranslational modification and for identifying O-linked glycoprotein fingerprints associated with disease. © 2006 by The National Academy of Sciences of the USA.

Date: 2020-06-03

Creator: Erik Nelson

Access: Open access

Glaeser et al. (2008) argue that the relative distribution of poor and rich households (HHs) in American cities is "strongly" explained by the spatial location of the cities' public transportation (PT) networks. Among their claims: 1) The broad distribution of poor and rich HHs in the typical American city is consistent with a basic monocentric city model that includes commute technology speeds; 2) Poor commuters will overwhelmingly transition from commuting by PT to car if they experience a substantial increase in their HH’s income; 3) areas in American cities that receive new PT infrastructure become poorer over time. Using 2017 data I find empirical evidence that partially or wholly contradicts these three claims. First, as of 2017, the observed concentration of poor HHs in the inner city and rich HHs in the suburbs of the US’ smaller cities cannot be explained by monocentric model that includes commute speeds. Second, as of 2017, significant increases in poor HHs’ incomes were not expected to lead to a "massive shift" towards car commuting in these HHs; most of these poor workers commute by car already. Third, using data from four cities that expanded their light-rail and rapid-bus network in the early 2000s, I find that neighborhoods surrounding new light-rail or rapid-bus stations either saw little change in their income patterns or became slightly richer after station opening. In conclusion, as of 2017, the spatial distribution of HH incomes within American urban areas is not as intricately linked to the location of PT networks as Glaeser et al. (2008) would have us believe. As an addendum to the analysis I add some thoughts on how the COVID-19 pandemic might affect commuting behavior and income distributions within urban areas over the next decade.

Date: 2010-12-02

Creator: William R. Jackman, James J. Yoo, David W. Stock

Access: Open access

Background. The accessibility of the developing zebrafish pharyngeal dentition makes it an advantageous system in which to study many aspects of tooth development from early initiation to late morphogenesis. In mammals, hedgehog signaling is known to be essential for multiple stages of odontogenesis; however, potential roles for the pathway during initiation of tooth development or in later morphogenesis are incompletely understood. Results. We have identified mRNA expression of the hedgehog ligands shha and the receptors ptc1 and ptc2 during zebrafish pharyngeal tooth development. We looked for, but did not detect, tooth germ expression of the other known zebrafish hedgehog ligands shhb, dhh, ihha, or ihhb, suggesting that as in mammals, only Shh participates in zebrafish tooth development. Supporting this idea, we found that morphological and gene expression evidence of tooth initiation is eliminated in shha mutant embryos, and that morpholino antisense oligonucleotide knockdown of shha, but not shhb, function prevents mature tooth formation. Hedgehog pathway inhibition with the antagonist compound cyclopamine affected tooth formation at each stage in which we applied it: arresting development at early stages and disrupting mature tooth morphology when applied later. These results suggest that hedgehog signaling is required continuously during odontogenesis. In contrast, over-expression of shha had no effect on the developing dentition, possibly because shha is normally extensively expressed in the zebrafish pharyngeal region. Conclusion. We have identified previously unknown requirements for hedgehog signaling for early tooth initiation and later morphogenesis. The similarity of our results with data from mouse and other vertebrates suggests that despite gene duplication and changes in the location of where teeth form, the roles of hedgehog signaling in tooth development have been largely conserved during evolution. © 2010 Jackman et al; licensee BioMed Central Ltd.

Date: 2018-01-01

Creator: Dallas G. Denery

Access: Open access

Date: 2019-06-12

Creator: Yann Gibert, Eric Samarut, Megan K. Ellis, William R. Jackman, Vincent, Laudet

Access: Open access

The diversity of teeth patterns in actinopterygians is impressive with tooth rows in many locations in the oral and pharyngeal regions. The first-formed tooth has been hypothesized to serve as an initiator controlling the formation of the subsequent teeth. In zebrafish, the existence of the first tooth (named 4 V1) is puzzling as its replacement is induced before the opening of the mouth. Functionally, it has been shown that 4 V1 formation requires fibroblast growth factor (FGF) and retinoic acid (RA) signalling. Here, we show that the ablation of 4 V1 prevents the development of the dental row demonstrating its dependency over it. If endogenous levels of FGF and RA are restored after 4 V1 ablation, embryonic dentition starts again by de novo formation of a first tooth, followed by the dental row. Similarly, induction of anterior ectopic teeth induces subsequent tooth formation, demonstrating that the initiator tooth is necessary and sufficient for dental row formation, probably via FGF ligands released by 4 V1 to induce the formation of subsequent teeth. Our results show that by modifying the formation of the initiator tooth it is possible to control the formation of a dental row. This could help to explain the diversity of tooth patterns observed in actinopterygians and more broadly, how diverse traits evolved through molecular fine-tuning.

Date: 2019-10-01

Creator: Belinda Kong

Access: Open access

This essay deploys the concept of pandemic as a set of discursive relations rather than a neutral description of a natural phenomenon, arguing that pandemic discourse is a product of layered histories of power that in turn reproduces myriad forms of imperial and racial power in the new millennium. The essay aims to denaturalize the idea of infectious disease by reframing it as an assemblage of multiple histories of American geopower and biopower from the Cold War to the War on Terror. In particular, Asia and Asian bodies have been targeted by US discourses of infection and biosecurity as frontiers of bioterrorism and the diseased other. A contemporary example of this bioorientalism can be seen around the 2003 SARS epidemic, in which global discourses projected the source of contagion onto Asia and Asians. Pandemic as method can thus serve as a theoretical pathway for examining cultural concatenations of orientalism and biopower.

Date: 2010-12-15

Creator: Yao Tang

Access: Open access

Although real currency appreciations pose direct difficulties for exporters and import-competing firms as they will face more intense competition, is it possible that such competition spurs firms to improve productivity? To answer this question, the paper first constructs a theoretical model to show how the competitive pressures of currency appreciations induce firms to improve productivity by adopting new technologies. In addition, the model predicts that during appreciations there will be a positive relation between market concentration and improvements in productivity for industries highly exposed to trade, because the marginal benefits of productivity improvement will be bigger for firms with a larger market share. The paper then examines Canadian manufacturing data from 1997 to 2006, and finds evidence consistent with model predictions. I find that growth rates of labor productivity were on average higher during the Canadian dollar appreciation between 2002 and 2006, after controlling for industry characteristics. Within the group of highly traded Canadian industries, the more concentrated ones experienced larger growth in labor productivity.

Date: 2021-02-01

Creator: J. E. Rheuban, P. R. Gassett, D. C. McCorkle, C. W. Hunt, M., Liebman, C. Bastidas, K. O’Brien-Clayton, A. R. Pimenta, E. Silva, P. Vlahos, R. J. Woosley, J. Ries, C. M. Liberti, J. Grear, J. Salisbury, D. C. Brady, K. Guay, M. LaVigne, A. L. Strong, E. Stancioff, E. Turner

Access: Open access

Comprehensive sampling of the carbonate system in estuaries and coastal waters can be difficult and expensive because of the complex and heterogeneous nature of near-shore environments. We show that sample collection by community science programs is a viable strategy for expanding estuarine carbonate system monitoring and prioritizing regions for more targeted assessment. ‘Shell Day’ was a single-day regional water monitoring event coordinating coastal carbonate chemistry observations by 59 community science programs and seven research institutions in the northeastern United States, in which 410 total alkalinity (TA) samples from 86 stations were collected. Field replicates collected at both low and high tides had a mean standard deviation between replicates of 3.6 ± 0.3 µmol kg (σ ± SE, n = 145) or 0.20 ± 0.02%. This level of precision demonstrates that with adequate protocols for sample collection, handling, storage, and analysis, community science programs are able to collect TA samples leading to high-quality analyses and data. Despite correlations between salinity, temperature, and TA observed at multiple spatial scales, empirical predictions of TA had relatively high root mean square error >48 µmol kg . Additionally, ten stations displayed tidal variability in TA that was not likely driven by low TA freshwater inputs. As such, TA cannot be predicted accurately from salinity using a single relationship across the northeastern US region, though predictions may be viable at more localized scales where consistent freshwater and seawater endmembers can be defined. There was a high degree of geographic heterogeneity in both mean and tidal variability in TA, and this single-day snapshot sampling identified three patterns driving variation in TA, with certain locations exhibiting increased risk of acidification. The success of Shell Day implies that similar community science based events could be conducted in other regions to not only expand understanding of the coastal carbonate system, but also provide a way to inventory monitoring assets, build partnerships with stakeholders, and expand education and outreach to a broader constituency. − 1 − 1 mean

Date: 2020-02-21

Creator: Daniel A. Williams, Kabita Pradhan, Ankita Paul, Ilana R. Olin, Owen T., Tuck, Karen D. Moulton, Suvarn S. Kulkarni, Danielle H. Dube

Access: Open access

The bacterial cell wall is a quintessential drug target due to its critical role in colonization of the host, pathogen survival, and immune evasion. The dense cell wall glycocalyx contains distinctive monosaccharides that are absent from human cells, and proper assembly of monosaccharides into higher-order glycans is critical for bacterial fitness and pathogenesis. However, the systematic study and inhibition of bacterial glycosylation enzymes remains challenging. Bacteria produce glycans containing rare deoxy amino sugars refractory to traditional glycan analysis, complicating the study of bacterial glycans and the creation of glycosylation inhibitors. To ease the study of bacterial glycan function in the absence of detailed structural or enzyme information, we crafted metabolic inhibitors based on rare bacterial monosaccharide scaffolds. Metabolic inhibitors were assessed for their ability to interfere with glycan biosynthesis and fitness in pathogenic and symbiotic bacterial species. Three metabolic inhibitors led to dramatic structural and functional defects in Helicobacter pylori. Strikingly, these inhibitors acted in a bacteria-selective manner. These metabolic inhibitors will provide a platform for systematic study of bacterial glycosylation enzymes not currently possible with existing tools. Moreover, their selectivity will provide a pathway for the development of novel, narrow-spectrum antibiotics to treat infectious disease. Our inhibition approach is general and will expedite the identification of bacterial glycan biosynthesis inhibitors in a range of systems, expanding the glycochemistry toolkit.

Date: 2013-04-01

Creator: Pornchai Kaewsapsak, Onyinyechi Esonu, Danielle H. Dube

Access: Open access

Due to the increased prevalence of bacterial strains that are resistant to existing antibiotics, there is an urgent need for new antibacterial strategies. Bacterial glycans are an attractive target for new treatments, as they are frequently linked to pathogenesis and contain distinctive structures that are absent in humans. We set out to develop a novel targeting strategy based on surface glycans present on the gastric pathogen Helicobacter pylori (Hp). In this study, metabolic labeling of bacterial glycans with an azide-containing sugar allowed selective delivery of immune stimulants to azide-covered Hp. We established that Hp's surface glycans are labeled by treatment with the metabolic substrate peracetylated N-azidoacetylglucosamine (Ac4GlcNAz). By contrast, mammalian cells treated with Ac4GlcNAz exhibited no incorporation of the chemical label within extracellular glycans. We further demonstrated that the Staudinger ligation between azides and phosphines proceeds under acidic conditions with only a small loss of efficiency. We then targeted azide-covered Hp with phosphines conjugated to the immune stimulant 2,4-dinitrophenyl (DNP), a compound capable of directing a host immune response against these cells. Finally, we report that immune effector cells catalyze selective damage in vitro to DNP-covered Hp in the presence of anti-DNP antibodies. The technology reported herein represents a novel strategy to target Hp based on its glycans. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Date: 2021-02-24

Creator: Umakant Mishra, Gustaf Hugelius, Eitan Shelef, Yuanhe Yang, Jens, Strauss, Alexey Lupachev, Jennifer W. Harden, Julie D. Jastrow, Chien Lu Ping, William J. Riley, Edward A.G. Schuur, Roser Matamala, Matthias Siewert, Lucas E. Nave, Charles D. Koven, Matthias Fuchs

Access: Open access

Large stocks of soil organic carbon (SOC) have accumulated in the Northern Hemisphere permafrost region, but their current amounts and future fate remain uncertain. By analyzing dataset combining >2700 soil profiles with environmental variables in a geospatial framework, we generated spatially explicit estimates of permafrost-region SOC stocks, quantified spatial heterogeneity, and identified key environmental predictors. We estimated that Pg C are stored in the top 3 m of permafrost region soils. The greatest uncertainties occurred in circumpolar toe-slope positions and in flat areas of the Tibetan region. We found that soil wetness index and elevation are the dominant topographic controllers and surface air temperature (circumpolar region) and precipitation (Tibetan region) are significant climatic controllers of SOC stocks. Our results provide first high-resolution geospatial assessment of permafrost region SOC stocks and their relationships with environmental factors, which are crucial for modeling the response of permafrost affected soils to changing climate.

Date: 2010-07-01

Creator: Anna Selmecki, Anja Forche, Judith Berman

Access: Open access

The genomic plasticity of Candida albicans, a commensal and common opportunistic fungal pathogen, continues to reveal unexpected surprises. Once thought to be asexual, we now know that the organism can generate genetic diversity through several mechanisms, including mating between cells of the opposite or of the same mating type and by a parasexual reduction in chromosome number that can be accompanied by recombination events (2, 12, 14, 53, 77, 115). In addition, dramatic genome changes can appear quite rapidly in mitotic cells propagated in vitro as well as in vivo. The detection of aneuploidy in other fungal pathogens isolated directly from patients (145) and from environmental samples (71) suggests that variations in chromosome organization and copy number are a common mechanism used by pathogenic fungi to rapidly generate diversity in response to stressful growth conditions, including, but not limited to, antifungal drug exposure. Since cancer cells often become polyploid and/or aneuploid, some of the lessons learned from studies of genome plasticity in C. albicans may provide important insights into how these processes occur in higher-eukaryotic cells exposed to stresses such as anticancer drugs. © 2010, American Society for Microbiology.

Date: 2012-01-01

Creator: Stephen M. Majercik

Access: Open access

Swarm intelligence can provide robust, adaptable, scalable solutions to difficult problems. The distributed nature of swarm activity is the basis of these desirable qualities, but it also prevents swarm-based techniques from having direct access to global knowledge that could facilitate the task at hand. Our experiments indicate that a swarm system can use an auxiliary swarm, called a communication swarm, to create and distribute an approximation of useful global knowledge, without sacrificing robustness, adaptability, and scalability. We describe a communication swarm and validate its effectiveness on a simple problem.

Date: 2017-07-14

Creator: Allison L. Dzubak, Jaron T. Krogel, Fernando A. Reboredo

Access: Open access

The necessarily approximate evaluation of non-local pseudopotentials in diffusion Monte Carlo (DMC) introduces localization errors. We estimate these errors for two families of non-local pseudopotentials for the first-row transition metal atoms Sc-Zn using an extrapolation scheme and multideterminant wavefunctions. Sensitivities of the error in the DMC energies to the Jastrow factor are used to estimate the quality of two sets of pseudopotentials with respect to locality error reduction. The locality approximation and T-moves scheme are also compared for accuracy of total energies. After estimating the removal of the locality and T-moves errors, we present the range of fixed-node energies between a single determinant description and a full valence multideterminant complete active space expansion. The results for these pseudopotentials agree with previous findings that the locality approximation is less sensitive to changes in the Jastrow than T-moves yielding more accurate total energies, however not necessarily more accurate energy differences. For both the locality approximation and T-moves, we find decreasing Jastrow sensitivity moving left to right across the series Sc-Zn. The recently generated pseudopotentials of Krogel et al. [Phys. Rev. B 93, 075143 (2016)] reduce the magnitude of the locality error compared with the pseudopotentials of Burkatzki et al. [J. Chem. Phys. 129, 164115 (2008)] by an average estimated 40% using the locality approximation. The estimated locality error is equivalent for both sets of pseudopotentials when T-moves is used. For the Sc-Zn atomic series with these pseudopotentials, and using up to three-body Jastrow factors, our results suggest that the fixed-node error is dominant over the locality error when a single determinant is used.

Date: 2019-01-01

Creator: Bess Vlaisavljevich, Sondre K. Schnell, Allison L. Dzubak, Kyuho Lee, Nora, Planas, Jeffrey B. Neaton, Laura Gagliardi, Berend Smit

Access: Open access

The authors regret that there are some discrepancies reproducing the data in the original article due to the determined coordinates not being the fully optimised geometries. The authors have provided more information as follows. In the manuscript entitled 'CO2 induced phase transitions in diamine-appended metal-organic frameworks', minor errors with the attached coordinates and energies reported in the paper have recently been identified. In this communication, we correct these errors. Here, we present updated optimized geometries and binding energies. We also take this opportunity to include an extended computational details section to ensure reproducibility. In addition, we show that the overall conclusions of the paper are not affected by these changes. A detailed comparison with the results reported by Lee et al.1 revealed that the DFT optimization of the coordinates provided with the manuscript do not lead to the values reported in the manuscript, and they warrant correction. Corrected coordinates and updated tables (Tables 1-7) and figures (Fig. 1, 2, 4 and 5) are included here for calculations using the PBE functional. These structures have been repeated using a slightly tighter force threshold than in the original manuscript (details below). The M06-L calculations reported in the original manuscript are not revisited since they were performed to assess the role of dispersion. Since the publication of our work in 2015, a far more detailed study of this effect has been published by one of the authors rendering these M06-L calculations unnecessary and we refer readers interested in the role of dispersion on the carbamate formation to this more recent study by Lee et al.1 In addition to correcting our DFT calculations, we examine the effects of the revised DFT values on the lattice model in this work.We recompute the lattice model with the M06-L and PBE values fromthe original manuscript as well as the corrected PBE values reported below (Fig. 6-8 and Tables 8-10). In all three sets of isotherm plots the ordering is preserved but the inflection points are spaced differently with the new PBE numbers, leading to quantitative differences that are nonetheless qualitatively similar to previous work. Finally, we discuss different ways that CO2 can coordinate to the metal binding site, as shown in Fig. 3. We should have notedmore clearly in ourmanuscript that these were starting configurations and not necessarily the final converged structures since our goal was to try several starting geometries to determine which coordination environment around the metal site was lowest in energy. Take for example bidentate insertion. Chemical intuition suggests that this structure could rotate to one that has only one CO2 oxygen center closer to the metal than the other and we observe this in our optimized structure. The resulting geometries we obtained for the starting arrangements noted in the figure are higher in energy than the chain model as reported in our original paper.We wish to emphasize that at the time of our 2015 study, our objective was to understand whether or not CO2 was bound to the metal and if one-dimensional chain formation could lead to a step in the adsorption isotherm. It has since become clear that a far more thorough study of the arrangements of the amines is required to truly understand competing amine arrangements preset in experiment. This was outside the scope of our work. Once more, these calculations are perhaps now outdated given work in the field in recent years. We again refer interested readers to a more recent study by Lee et al.1 1. Extended computational details to ensure reproducibility In the course of rectifying the error in our calculations, we wanted to ensure that all revised calculations were converged using the exact same protocol; therefore, we repeated the PBE calculations for the pair and chain models using updated computational details given here to ensure reproducibility. The M2(dobpdc) MOF contains six unsaturated metal sites per unit cell. To calculate the binding energies of CO2 in its amine appended analogue mmen-M2(dobpdc), one mmen ligand per CO2 was added per unit cell. The smaller sized ethylenediamine (en) was used to saturate the remaining amines not involved in CO2 binding. In the case of the pair mode, two mmen-amines are included per unit cell only. All DFT calculations were performed with periodic boundary conditions carried out using the VASP 5.4.4 package (original calculations were performed with VASP 5.3.3). The PBE functional was employed to examine the energetics of CO2 adsorption.3 On-site Hubbard U corrections were employed for metal d electrons.4 The U values are determined to reproduce oxidation energies in the respective metal oxides and are given in the tables below. The electron-ion interactions in these calculations were described with the projector augmented wave (PAW) method developed by Blöchl with an energy cutoff of 550 eV.5 This combination of the PBE functional, PAW scheme, and energy cutoff was used for full geometry optimization of the various species investigated until the forces on all atoms were smaller than 0.02 eV Å-1 and the SCF convergence was set to 1 × 10-7 eV. Given the large size of the unit cell and the tests with other numbers of K-points from the original study, only results obtained from G-point calculations are reported here. Finally, heats of adsorption are now reported below along with E + ZPE values, while in the original manuscript only E + ZPE were reported. No changes were made to how the vibrational corrections were computed; however, we have included some additional details to ensure reproducibility.6 Harmonic vibrational modes (ωi) were computed for CO2 in the gas phase and its bound product state (amine-CO2-MOF complex). The framework itself was taken to be rigid and only the vibrational modes associated with the motion of the amine, the metal center, first coordination sphere (oxygen atoms bound to the metal in the MOF backbone), and (if present) the bound CO2 were computed. Since the harmonic approximation breaks down for low frequency modes, we replaced all modes less than 50 cm-1 with 50 cm-1 when computing the zero-point and thermal energies. The following standard harmonic expressions were used to compute the vibrational corrections: Zero-point vibrational energy (ZPE) is: [Equation presented here] While for the bound product, the rotational and translational degrees of freedom of CO2 have been converted to additional vibrational modes allowing one to compute the thermal correction simply as: [Equation presented here] 2. Values for the chain model The chain model used in our original study included 1 mmen- and 5 en-amines. The values from the original paper are reported in Table 1. When we repeat these calculations using the procedure described in Section 1, we obtain the values in Table 2. In addition to the chain model described above (1 mmen- and 5 en-amines per unit cell), during our original study we performed calculations with another model that was not included in the manuscript since its values yielded results further from experiment. This model includes only 1 mmen-amine per unit cell (no other amines) and was used to test the assumption that the five enamines are indeed spectators with respect to the metal dependence of the binding energy. We present the results from this model in Table 3. In the original paper we noted that the energy and bond length trends are correlated and are consistent with the Irving-Williams series. This is no longer true for all metals under investigation, with Zn being an outlier. The results for Zn can be explained by more recent work.1 3. Values for the pair model The model used to compute the "pair" adsorption mechanisms included 2 mmen-amines and 0 en-amines. The values in the original paper are presented in Table 5. 4. Lattice model plots The lattice models to generate adsorption isotherms for these systems were run at one temperature (∼25 °C) using four different input parameters. First the M06-L and PBE values from the original paper were used once more as it has been some time since we have run the lattice model. Then the model is repeated with the new set of values from PBE. If we compare Fig. 7 and 8, the order is preserved, but the infliction points are spaced a bit differently. This is due to the scaling factor being constant and is something we scaled for each of the different systems as well. The slope is also a bit different, but not more then we should expect for this simple lattice model. Furthermore, we only ever aimed to reproduce the step and the order of the metals. Any finer details cannot be expected to be obtained from this model. The exact values used to compute the isotherms are given in the tables below. The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.

Date: 2019-12-01

Creator: Courtney M. Payne, Collin S. Roesler

Access: Open access

Warm water intrusion into Arctic fjords is increasingly affecting polar ecosystems. This study investigated how Atlantic water intrusion and tidewater glacial melting impacted water mass formation and phytoplankton distribution in Kongsfjorden, Svalbard. Field data were collected over a 2-week period during the height of the melt season in August 2014 and were contextualized within an 18-year regional MODIS satellite record. Since 1998, intruding waters have warmed by 4–5.5 °C, which has prevented sea ice formation and changed the characteristics of fjord bottom waters. Modeled light fields suggest that suspended sediment in this glacial meltwater has reduced the euphotic zone close to the ice face, contributing to lower phytoplankton concentrations in both persistent and intermittently sediment-laden meltwater plumes. However, measurements collected close to terrestrially terminating glaciers indicate that turbidity is significantly lower in the meltwater plumes, resulting in deep euphotic zones and high phytoplankton concentrations. The results of this study support a three-part conceptual model of the effects of warm-water intrusion on water mass formation and primary production within 10 km of tidewater glaciers. Initially, warm water intrusion reduces sea ice coverage, which increases the euphotic depth and increases phytoplankton biomass. Warm water intrusions may also result in increased melting of tidewater glaciers, enhanced sediment release, reduction in euphotic depth and reduction in phytoplankton biomass. Ultimately, as tidewater glaciers retreat and become terrestrially terminating, the sediment load decreases, the euphotic zone again increases, and phytoplankton biomass increases.

Date: 2019-01-01

Creator: Kathleen James-Chakraborty, Pep Avilés, Claudia Tittel, Jill Pearlman

Access: Open access

Date: 2018-02-01

Creator: Erika Nyhus

Access: Open access

Evidence from fMRI has consistently located a widespread network of frontal, parietal, and temporal lobe regions during episodic retrieval. However, the temporal limitations of the fMRI methodology have made it difficult to assess the transient network dynamics by which these distributed regions coordinate activity. Recent evidence suggests that beta oscillations (17-20 Hz) are important for top-down control for memory suppression. However, the spatial limitations of the EEG methodology make it difficult to assess the relationship between these oscillatory signals and the distributed networks identified with fMRI. This study used simultaneous EEG/fMRI to identify networks related to beta oscillations during episodic retrieval. Participants studied adjectives and either imagined a scene (Place Task) or judged its pleasantness (Pleasant Task). During the recognition test, participants decided which task was performed with each word (“Old Place Task” or “Old Pleasant Task”) or “New.” EEG results revealed that posterior beta power was greater for new than old words. fMRI results revealed activity in a frontal, parietal network that was greater for old than new words, consistent with prior studies. Although overall beta power increases correlated with decreased activity within a predominantly parietal network, within the right dorsolateral and ventrolateral pFC, beta power correlated with BOLD activity more under conditions requiring more cognitive control and EEG/fMRI effects in the right frontal cortex correlated with BOLD activity in a frontoparietal network. Therefore, using simultaneous EEG and fMRI, the present results suggest that beta oscillations are related to postretrieval control operations in the right frontal cortex and act within a broader postretrieval control network. © 2017 Massachusetts Institute of Technology.

Date: 2022-06-01

Creator: Syanah C. Wynn, Erika Nyhus, Ole Jensen

Access: Open access

To successfully encode information into long-term memory, we need top-down control to focus our attention on target stimuli. This attentional focus is achieved by the modulation of sensory neuronal excitability through alpha power. Failure to modulate alpha power and to inhibit distracting information has been reported in older adults during attention and working memory tasks. Given that alpha power during encoding can predict subsequent memory performance, aberrant oscillatory modulations might play a role in age-related memory deficits. However, it is unknown whether there are age-related differences in memory performance or alpha modulation when encoding targets with distraction. Here we show that both older and younger adults are able to encode targets paired with distractors and that the level of alpha power modulation during encoding predicted recognition success. Even though older adults showed signs of higher distractibility, this did not harm their episodic memory for target information. Also, we demonstrate that older adults only modulated alpha power during high distraction, both by enhancing target processing and inhibiting distractor processing. These results indicate that both younger and older adults are able to employ the same inhibitory control mechanisms successfully, but that older adults fail to call upon these when distraction is minimal. The findings of this study give us more insight into the mechanisms involved in memory encoding across the lifespan. © 2020 Federation of European Neuroscience Societies and John Wiley & Sons Ltd.

Date: 2016-01-01

Creator: C. C. Treat, M. C. Jones, P. Camill, A. Gallego-Sala, M., Garneau, J. W. Harden, G. Hugelius, E. S. Klein, U. Kokfelt, P. Kuhry, J. Loisel, P. J.H. Mathijssen, J. A. O'Donnell, P. O. Oksanen, T. M. Ronkainen, A. B.K. Sannel

Access: Open access

Permafrost dynamics play an important role in high-latitude peatland carbon balance and are key to understanding the future response of soil carbon stocks. Permafrost aggradation can control the magnitude of the carbon feedback in peatlands through effects on peat properties. We compiled peatland plant macrofossil records for the northern permafrost zone (515 cores from 280 sites) and classified samples by vegetation type and environmental class (fen, bog, tundra and boreal permafrost, and thawed permafrost). We examined differences in peat properties (bulk density, carbon (C), nitrogen (N) and organic matter content, and C/N ratio) and C accumulation rates among vegetation types and environmental classes. Consequences of permafrost aggradation differed between boreal and tundra biomes, including differences in vegetation composition, C/N ratios, and N content. The vegetation composition of tundra permafrost peatlands was similar to permafrost-free fens, while boreal permafrost peatlands more closely resembled permafrost-free bogs. Nitrogen content in boreal permafrost and thawed permafrost peatlands was significantly lower than in permafrost-free bogs despite similar vegetation types (0.9% versus 1.5% N). Median long-term C accumulation rates were higher in fens (23 g C m yr ) than in permafrost-free bogs (18 g C m yr ) and were lowest in boreal permafrost peatlands (14 g C m yr ). The plant macrofossil record demonstrated transitions from fens to bogs to permafrost peatlands, bogs to fens, permafrost aggradation within fens, and permafrost thaw and reaggradation. Using data synthesis, we have identified predominant peatland successional pathways, changes in vegetation type, peat properties, and C accumulation rates associated with permafrost aggradation. -2 -1 -2 -1 -2 -1

Date: 2020-06-01

Creator: Marcel Garz, Gaurav Sood, Daniel F. Stone, Justin Wallace

Access: Open access

We conduct across-outlet and within-outlet (and within-topic) analyses of “congenially” slanted news. We study “horse race” news (news on candidates' chances in an upcoming election) from six major online outlets for the 2012 and 2016 US presidential campaigns. We find robust evidence that horse race headlines were slanted congenially with respect to the preferences of the outlets' typical readers. However, evidence of congenial slant in the timing and frequency of horse race stories is weaker. We also find limited evidence of greater within-outlet demand for headlines most congenial to outlets' typical readers, and somewhat stronger evidence of greater demand for relatively uncongenial headlines. We discuss how various aspects of our results are consistent with each of the major mechanisms driving slant studied in the theoretical literature, and may help explain when each mechanism is more likely to come into play. In particular, readers may be more likely to click on uncongenial headlines due to inferring that these stories are particularly informative when they stand in contrast to an outlet's typically congenial slant.

Date: 2015-01-01

Creator: Charles E. Umbanhowar, Philip Camill, Mark B. Edlund, Christoph Geiss, Patrick, Henneghan, Kendra Passow

Access: Open access

To better understand aquatic-terrestrial linkages in the sub-Arctic, and specifically the relative importance of landscape position versus land cover, we surveyed lakes, soils, land cover, and lake/basin characteristics in a 14000 km region of acidic forest-tundra landscape near northern Manitoba, Canada (59.56°N, 97.72°W) in 2009. We analyzed 39 different biological, chemical, and physical variables for lakes and soils. We used a remote-sensing-based classification to determine that the landscape was 21% water, 46% peat-forming lowland, and 24.9% open tundra, and we assigned lake order to all lakes based on the order of the outlet stream for each lake. Lakes were oligotrophic to mesotrophic (median total phosphorus: TP = 11.8 μg L ), N-limited (median dissolved inorganic nitrogen: TP = 1.6), acidic (median pH 5.7), and had moderate amounts of dissolved organic carbon (median DOC = 5.2 mg L ). We identified 2 principle groups of variables represented by DOC and conductivity/ cations, respectively, that captured major axes of lake variation. DOC, 2 measures of DOC quality (a /a [a proxy for molecular weight and aromaticity] and specific ultraviolet absorbance), and Fe and were significantly correlated with percent cover of lowland forest, but conductivity/cations were not correlated with variation in land cover. Soils were generally acidic (pH 2.7-4.4) and nutrient-poor, and wetland soils contained more carbon and higher concentrations of calcium, magnesium, and other cations than upland open tundra. Landscape position of lakes (measured as lake order) did not capture systematic differences in land cover or lake biogeochemistry. Our results highlight the importance of lowland export of DOC to lakes and further suggest the need for additional regional studies of aquatic-terrestrial connections in Arctic and sub-Arctic landscapes. 2 -1 -1 250 365

Date: 2009-12-01

Creator: Vivian Caroline Klein, Samuel P. Putnam, Maria Beatriz Martins Linhares

Access: Open access

International research has increasingly considered temperament as a relevant personal variable in child developmental pathways. The purpose of the present study was to describe the methodology for translation to Portuguese (Brazil) of three child temperament assessment instruments based on Rothbart's theoretical approach. An original translation was modified, based on feedback by two professional translators, three bilingual psychologists, and a sample of 15 Brazilian mothers. A backtranslation by a professional translator was then assessed by the authors of the original (English language) instruments. For the final version of the measure, authors of the original instrument judged that 100% of items were consistent with the original items, and a second sample of 15 Brazilian mothers identified no problems with the Portuguese items.

Date: 2006-07-01

Creator: Samuel P. Putnam, Maria A. Gartstein, Mary K. Rothbart

Access: Open access

This article describes the development, reliability, and factor structure of a finely differentiated (18 dimensions) parent-report measure of temperament in 1.5- to 3-year-old children, using a cross-sectional sample (N = 317) and a longitudinal sample of primary (N = 104) and secondary (N = 61) caregivers. Adequate internal consistency was demonstrated for all scales and moderate inter-rater reliability was evident for most scales. Longitudinal stability correlations were primarily large over 6- and 12-month spans and moderate to large from 18 to 36 months. Factor analysis revealed a three-factor structure of Surgency/Extraversion, Negative Affectivity, and Effortful Control. In both samples and for both primary and secondary caregivers, older children received higher scores for Attention Focusing, Discomfort, Inhibitory Control, and Positive Anticipation. Primary caregivers rated females higher in Fear, and lower in High-intensity Pleasure, than males; secondary caregivers rated females higher than males in several aspects of Effortful Control. © 2006 Elsevier Inc. All rights reserved.

Date: 2006-04-01

Creator: R. Carretero-González, J. D. Talley, C. Chong, B. A. Malomed

Access: Open access

We analyze the existence and stability of localized solutions in the one-dimensional discrete nonlinear Schrödinger (DNLS) equation with a combination of competing self-focusing cubic and defocusing quintic onsite nonlinearities. We produce a stability diagram for different families of soliton solutions that suggests the (co)existence of infinitely many branches of stable localized solutions. Bifurcations that occur with an increase in the coupling constant are studied in a numerical form. A variational approximation is developed for accurate prediction of the most fundamental and next-order solitons, together with their bifurcations. Salient properties of the model, which distinguish it from the well-known cubic DNLS equation, are the existence of two different types of symmetric solitons and stable asymmetric soliton solutions that are found in narrow regions of the parameter space. The asymmetric solutions appear from and disappear back into the symmetric ones via loops of forward and backward pitchfork bifurcations. © 2006 Elsevier Ltd. All rights reserved.

Date: 2010-01-01

Creator: Thomas Pietraho

Access: Open access

We describe a map relating hyperoctahedral Robinson-Schensted algorithms on standard domino tableaux of unequal rank. Iteration of this map relates the algorithms defined by Garfinkle and Stanton-White and when restricted to involutions, this construction answers a question posed by van Leeuwen. The principal technique is derived from operations defined on standard domino tableaux by Garfinkle which must be extended to this more general setting. © Birkhäuser Verlag Basel/Switzerland 2009.

Date: 2001-01-01

Creator: B. Zorina Khan, Kenneth L. Sokoloff

Access: Open access

Date: 2016-12-01

Creator: Erika Franklin Fowler, Travis N. Ridout, Michael M. Franz

Access: Open access

The 2016 presidential campaign broke the mold when it comes to patterns of political advertising. Using data from the Wesleyan Media Project, we show the race featured far less advertising than the previous cycle, a huge imbalance in the number of ads across candidates and one candidate who almost ignored discussions of policy. This departure from past patterns, however, was not replicated at the congressional level. We draw some lessons about advertising from the 2016 campaign, suggesting that its seeming lack of effectiveness may owe to the unusual nature of the presidential campaign with one unconventional candidate and the other using an unconventional message strategy, among other non-advertising related factors.

Date: 2016-11-01

Creator: Aba Mbirika, Thomas Pietraho, William Silver

Access: Open access

We present a formula for the values of the sign representations of a complex reflection group G(r, p, n) in terms of its image under a generalized Robinson–Schensted algorithm.

Date: 1998-01-01

Creator: Olaf Ellers, Amy S. Johnson, Philip E. Moberg

Access: Open access

Sea urchin skeletons are strengthened by flexible collagenous ligaments that bind together rigid calcite plates at sutures. Whole skeletons without ligaments (removed by bleaching) broke at lower apically applied forces than did intact, fresh skeletons. In addition, in three-point bending tests on excised plate combinations, sutural ligaments strengthened sutures but not plates. The degree of sutural strengthening by ligaments depended on sutural position; in tensile tests, ambital and adapical sutures were strengthened more than adoral sutures. Adapical sutures, which grow fastest, were also the loosest, suggesting that strengthening by ligaments is associated with growth. In fed, growing urchins, sutures overall were looser than in unfed urchins. Looseness was demonstrated visually and by vibration analysis: bleached skeletons of unfed urchins rang at characteristic frequencies, indicating that sound traveled across tightly fitting sutures; skeletons of fed urchins damped vibrations, indicating loss of vibrational energy across looser sutures. Furthermore, bleached skeletons of fed urchins broke at lower apically applied forces than bleached skeletons of unfed urchins, indicating that the sutures of fed urchins had been held together relatively loosely by sutural ligaments. Thus, the apparently rigid dome-like skeleton of urchins sometimes transforms into a flexible, jointed membrane as sutures loosen and become flexible during growth.

Date: 2013-04-08

Creator: C. Chong, P. G. Kevrekidis, G. Theocharis, Chiara Daraio

Access: Open access

We present a study of the existence, stability, and bifurcation structure of families of dark breathers in a one-dimensional uniform chain of spherical beads under static load. A defocusing nonlinear Schrödinger equation (NLS) is derived for frequencies that are close to the edge of the phonon band and is used to construct targeted initial conditions for numerical computations. Salient features of the system include the existence of large amplitude solutions that emerge from the small amplitude solutions described by the NLS equation, and the presence of a nonlinear instability that, to the best of the authors' knowledge, has not been observed in classical Fermi-Pasta-Ulam lattices. Finally, it is also demonstrated that these dark breathers can be detected in a physically realistic experimental settings by merely actuating the ends of an initially at rest chain of beads and inducing destructive interference between their signals. © 2013 American Physical Society.

Date: 2021-05-01

Creator: Bruce D. Kohorn, Bridgid E. Greed, Gregory Mouille, Stéphane Verger, Susan L., Kohorn

Access: Open access

Angiosperm cell adhesion is dependent on interactions between pectin polysaccharides which make up a significant portion of the plant cell wall. Cell adhesion in Arabidopsis may also be regulated through a pectin-related signaling cascade mediated by a putative O-fucosyltransferase ESMERALDA1 (ESMD1), and the Epidermal Growth Factor (EGF) domains of the pectin binding Wall associated Kinases (WAKs) are a primary candidate substrate for ESMD1 activity. Genetic interactions between WAKs and ESMD1 were examined using a dominant hyperactive allele of WAK2, WAK2cTAP, and a mutant of the putative O-fucosyltransferase ESMD1. WAK2cTAP expression results in a dwarf phenotype and activation of the stress response and reactive oxygen species (ROS) production, while esmd1 is a suppressor of a pectin deficiency induced loss of adhesion. Here we find that esmd1 suppresses the WAK2cTAP dwarf and stress response phenotype, including ROS accumulation and gene expression. Additional analysis suggests that mutations of the potential WAK EGF O-fucosylation site also abate the WAK2cTAP phenotype, yet only evidence for an N-linked but not O-linked sugar addition can be found. Moreover, a WAK locus deletion allele has no effect on the ability of esmd1 to suppress an adhesion deficiency, indicating WAKs and their modification are not a required component of the potential ESMD1 signaling mechanism involved in the control of cell adhesion. The WAK locus deletion does however affect the induction of ROS but not the transcriptional response induced by the elicitors Flagellin, Chitin and oligogalacturonides (OGs).

Date: 2016-01-01

Creator: E. S. Dickinson, A. S. Johnson, O. Ellers, P. S. Dickinson

Access: Open access

Mechanical and neurophysiological anisotropies mediate three-dimensional responses of the heart of Homarus americanus. Although hearts in vivo are loaded multi-axially by pressure, studies of invertebrate cardiac function typically use uniaxial tests. To generate whole-heart length-tension curves, stretch pyramids at constant lengthening and shortening rates were imposed uniaxially and biaxially along longitudinal and transverse axes of the beating whole heart. To determine whether neuropeptides that are known to modulate cardiac activity in H. americanus affect the active or passive components of these length-tension curves, we also performed these tests in the presence of SGRNFLRFamide (SGRN) and GYSNRNYLRFamide (GYS). In uniaxial and biaxial tests, both passive and active forces increased with stretch along both measurement axes. The increase in passive forces was anisotropic, with greater increases along the longitudinal axis. Passive forces showed hysteresis and active forces were higher during lengthening than shortening phases of the stretch pyramid. Active forces at a given length were increased by both neuropeptides. To exert these effects, neuropeptides might have acted indirectly on the muscle via their effects on the cardiac ganglion, directly on the neuromuscular junction, or directly on the muscles. Because increases in response to stretch were also seen in stimulated motor nerve-muscle preparations, at least some of the effects of the peptides are likely peripheral. Taken together, these findings suggest that flexibility in rhythmic cardiac contractions results from the amplified effects of neuropeptides interacting with the length-tension characteristics of the heart.

Date: 2017-11-01

Creator: Joyce Weeland, Alithe Van den Akker, Meike Slagt, Samuel Putnam

Access: Open access

When interacting with other people, both children's biological predispositions and past experiences play a role in how they will process and respond to social–emotional cues. Children may partly differ in their reactions to such cues because they differ in the threshold for perceiving such cues in general. Theoretically, perceptual sensitivity (i.e., the amount of detection of slight, low-intensity stimuli from the external environment independent of visual and auditory ability) might, therefore, provide us with specific information on individual differences in susceptibility to the environment. However, the temperament trait of perceptual sensitivity is highly understudied. In an experiment, we tested whether school-aged children's (N = 521, 52.5% boys, Mage = 9.72 years, SD = 1.51) motor (facial electromyography) and affective (self-report) reactivities to dynamic facial expressions and vocalizations is predicted by their (parent-reported) perceptual sensitivity. Our results indicate that children's perceptual sensitivity predicts their motor reactivity to both happy and angry expressions and vocalizations. In addition, perceptual sensitivity interacted with positive (but not negative) parenting behavior in predicting children's motor reactivity to these emotions. Our findings suggest that perceptual sensitivity might indeed provide us with information on individual differences in reactivity to social–emotional cues, both alone and in interaction with parenting behavior. Because perceptual sensitivity focuses specifically on whether children perceive cues from their environment, and not on whether these cues cause arousal and/or whether children are able to regulate this arousal, it should be considered that perceptual sensitivity lies at the root of such individual differences.

Date: 2015-11-01

Creator: Jennifer Taback, Sharif Younes

Access: Open access

The definition of graph automatic groups by Kharlampovich, Khoussainov and Miasnikov and its extension to C-graph automatic by Elder and the first author raise the question of whether Thompson's group F is graph automatic. We define a language of normal forms based on the combinatorial "caret types", which arise when elements of F are considered as pairs of finite rooted binary trees. The language is accepted by a finite state machine with two counters, and forms the basis of a 3-counter graph automatic structure for the group.

Date: 2015-05-20

Creator: Jay J. Falk, Hannah M. Ter Hofstede, Patricia L. Jones, Marjorie M. Dixon, Paul A., Faure, Elisabeth K.V. Kalko, Rachel A. Page

Access: Open access

Many predators and parasites eavesdrop on the communication signals of their prey. Eavesdropping is typically studied as dyadic predator-prey species interactions; yet in nature, most predators target multiple prey species and most prey must evade multiple predator species. The impact of predator communities on prey signal evolution is not well understood. Predators could converge in their preferences for conspicuous signal properties, generating competition among predators and natural selection on particular prey signal features. Alternatively, predator species could vary in their preferences for prey signal properties, resulting in sensory-based niche partitioning of prey resources. In the Neotropics, many substrate-gleaning bats use the mate-attraction songs of male katydids to locate them as prey. We studied mechanisms of niche partitioning in four substrate- gleaning bat species and found they are similar in morphology, echolocation signal design and prey-handling ability, but each species preferred different acoustic features of male song in 12 sympatric katydid species. This divergence in predator preference probably contributes to the coexistence of many substrate-gleaning bat species in the Neotropics, and the substantial diversity in the mate-attraction signals of katydids. Our results provide insight into how multiple eavesdropping predator species might influence prey signal evolution through sensory-based niche partitioning.

Date: 1999-04-02

Creator: Shaun Snyders, Bruce D. Kohorn

Access: Open access

The phosphorylation of proteins within the eukaryotic photosynthetic membrane is thought to regulate a number of photosynthetic processes in land plants and algae. Both light quality and intensity influence protein kinase activity via the levels of reductants produced by the thylakoid electron transport chain. We have isolated a family of proteins called TAKs, Arabidopsis thylakoid membrane threonine kinases that phosphorylate the light harvesting complex proteins. TAK activity is enhanced by reductant and is associated with the photosynthetic reaction center II and the cytochrome b6f complex. TAKs are encoded by a gene family that has striking similarity to transforming growth factor β receptors of metazoans. Thus thylakoid protein phosphorylation may be regulated by a cascade of reductant-controlled membrane-bound protein kinases.