Showing 2101 - 2110 of 5708 Items
Consequences of a flattened morphology: effects of flow on feeding rates of the scleractinian coral Meandrina meandrites
Date: 1993-01-01
Creator: A. S. Johnson, K. P. Sebens
Access: Open access
- Per polyp feeding rate was independent of the horizontal planform area of colonies. At the lowest velocities, most particles were captured on the upstream edge or in the middle of colonies, but all positional bias in capture rate disappeared at higher velocities. Particle capture and increasing flow speed were negatively associated. There were small, but measurable, differences in mean tentacle length between corals feeding at different velocities. Velocity-dependent feeding rate at most velocities was thus related to changes in flow rather than to changes in feeding behavior. Experiments in which corals were turned upside down revealed that the increased capture rate for rightside-up corals feeding at low velocity could be almost entirely accounted for by gravitational deposition of particles on the corals' tentacles. The tentacles form a canopy within which water movement was slowed, possibly facilitating gravitational deposition of non-buoyant or sinking food particles. -from Authors
FMRI and EEG predictors of dynamic decision parameters during human reinforcement learning
Date: 2015-01-01
Creator: Michael J. Frank, Chris Gagne, Erika Nyhus, Sean Masters, Thomas V., Wiecki, James F. Cavanagh, David Badre
Access: Open access
- What are the neural dynamics of choice processes during reinforcement learning? Two largely separate literatures have examined dynamics of reinforcement learning (RL) as a function of experience but assuming a static choice process, or conversely, the dynamics of choice processes in decision making but based on static decision values. Here we show that human choice processes during RL are well described by a drift diffusion model (DDM) of decision making in which the learned trial-by-trial reward values are sequentially sampled, with a choice made when the value signal crosses a decision threshold. Moreover, simultaneous fMRI and EEG recordings revealed that this decision threshold is not fixed across trials but varies as a function of activity in the subthalamic nucleus (STN) and is further modulated by trial-by-trial measures of decision conflict and activity in the dorsomedial frontal cortex (pre-SMABOLDand mediofrontal theta in EEG). These findings provide converging multimodal evidence for a model in which decision threshold in reward-based tasks is adjusted as a function of communication from pre-SMA to STN when choices differ subtly in reward values, allowing more time to choose the statistically more rewarding option.
One-loop SYM-supergravity relation for five-point amplitudes
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.
Haplotype mapping of a diploid non-meiotic organism using existing and induced aneuploidies
Date: 2008-01-01
Creator: Melanie Legrand, Anja Forche, Anna Selmecki, Christine Chan, David T., Kirkpatrick, Judith Berman
Access: Open access
- Haplotype maps (HapMaps) reveal underlying sequence variation and facilitate the study of recombination and genetic diversity. In general, HapMaps are produced by analysis of Single-Nucleotide Polymorphism (SNP) segregation in large numbers of meiotic progeny. Candida albicans, the most common human fungal pathogen, is an obligate diploid that does not appear to undergo meiosis. Thus, standard methods for haplotype mapping cannot be used. We exploited naturally occurring aneuploid strains to determine the haplotypes of the eight chromosome pairs in the C. albicans laboratory strain SC5314 and in a clinical isolate. Comparison of the maps revealed that the clinical strain had undergone a significant amount of genome rearrangement, consisting primarily of crossover or gene conversion recombination events. SNP map haplotyping revealed that insertion and activation of the UAU1 cassette in essential and non-essential genes can result in whole chromosome aneuploidy. UAU1 is often used to construct homozygous deletions of targeted genes in C. albicans; the exact mechanism (trisomy followed by chromosome loss versus gene conversion) has not been determined. UAU1 insertion into the essential ORC1 gene resulted in a large proportion of trisomic strains, while gene conversion events predominated when UAU1 was inserted into the non-essential LRO1 gene. Therefore, induced aneuploidies can be used to generate HapMaps, which are essential for analyzing genome alterations and mitotic recombination events in this clonal organism. © 2008 Legrand et al.
Spending Fast and Furious: Political Advertising in 2020
Date: 2021-03-01
Creator: Travis N. Ridout, Erika Franklin Fowler, Michael M. Franz
Access: Open access
- This article is a "first look"at political advertising in 2020. Spending on political advertising in the United States in 2020 obliterated records, and Democrats held huge advantages in the presidential race and in most congressional and senatorial races. In addition, all indicators suggest that spending on digital advertising continued to rise. Political advertising was largely similar in tone to past years and, in the presidential race, was substantially more positive than 2016. In addition, interest groups remained heavily involved in federal races in 2020, airing more ads than ever before, though their spending as a percentage of total ad spending was slightly less than in 2016. Political ad spending in 2020 may have been historically high because of the impact of COVID-19 on how campaigns could reach voters, suggesting that paid advertising may decline in 2022 and 2024, at least as a percentage of total election spending.
Carbon and hydrogen isotopic composition of methane over the last 1000 years
Date: 2009-10-01
Creator: J. A. Mischler, T. A. Sowers, R. B. Alley, M. Battle, J. R., McConnell, L. Mitchell, T. Popp, E. Sofen, M. K. Spencer
Access: Open access
- New measurements of the carbon and hydrogen isotopic ratios of methane (δ13 C of CH4 and δD of CH4) over the last millennium are presented from the WAIS Divide, Antarctica, ice core (WDC05A), showing significant changes that likely were the result of human influences prior to the industrial revolution (at least as early as the 16th century of the common era (CE)). The (δ13C of CH4 data corroborate the record from Law Dome, Antarctica, with high fidelity. The new δD of CH4 data set covaries with the (δ13C of CH4 record. Both (δ13C of CH4 and δD of CH4 were relatively stable and close to the present-day values from ∼to ∼CE. Both isotopic ratios decreased to minima around 1700 CE, remained low until the late 18th century, and then rose exponentially to present-day values. Our new δD of CH4 data provide an additional independent constraint for evaluating possible CH4 source histories. We searched a broad range of source scenarios using a simple box model to identify histories consistent with the constraints of the CH 4 concentration and isotope data from 990-1730 CE. Results typically show a decrease over time in the biomass-burning source (found in 85% of acceptable scenarios) and an increase in the agricultural source (found in 77% of acceptable scenarios), indicating preindustrial human influence on atmospheric methane as proposed in previous studies. © 2009 by the American Geophysical Union.
Higgs-regularized three-loop four-gluon amplitude in N = 4 SYM: Exponentiation and Regge limits
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.
Tapping at the Windows: A Collection This record is embargoed.
- Embargo End Date: 2025-05-14
Date: 2020-01-01
Creator: Samuel Milligan
Access: Embargoed