Showing 701 - 710 of 2039 Items
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.
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.
Eikonal methods applied to gravitational scattering amplitudes
Date: 2011-01-01
Creator: Stephen G. Naculicha
Howard J. Schnitzerb
Access: Open access
- We apply factorization and eikonal methods from gauge theories to scattering amplitudes in gravity. We hypothesize that these amplitudes factor into an IR-divergent soft function and an IR-finite hard function, with the former given by the expectation value of a product of gravitational Wilson line operators. Using this approach, we show that the IR-divergent part of the n-graviton scattering amplitude is given by the exponential of the one-loop IR divergence, as originally discovered byWeinberg, with no additional subleading IR-divergent contributions in dimensional regularization. © SISSA 2011.
Social support buffers the effects of maternal prenatal stress on infants' unpredictability
Date: 2021-06-01
Creator: Lea Takács
Jiří Štipl
Maria Gartstein
Samuel P. Putnam
Catherine, Monk
Access: Open access
- Objective: Exposure to stress in pregnancy has been shown to affect fetal development with short- and long-term physiological and behavioral consequences for the offspring. Although social support is known to lower perceived stress, no prior study has investigated the buffering role of social support in the context of prenatal stress effects on infant temperament. The aim of this study was to examine interactive effects of prenatal stress and social support on several dimensions of infant temperament at 9 months postpartum. Study design: A total of 272 mothers completed the Perceived Stress Scale and the Perceived Social Support Scale in the 3rd trimester of pregnancy. Infant temperament was assessed by mothers at 9 months postpartum using the Infant Characteristics Questionnaire. Linear regression models were performed to assess the effects of perceived stress, social support, and their interaction on infant temperament. Results: Prenatal stress interacted with social support, such that prenatal stress increased infant unpredictability when social support was below -0.5 SD. Conclusions: Prenatal stress was found to be a risk factor for infant temperamental unpredictability when combined with low social support perceived by the mother during pregnancy. Support of others, not previously examined in this context, can reduce the impact of prenatal stress.
More loops and legs in Higgs-regulated N = 4 SYM amplitudes
Date: 2010-01-01
Creator: Johannes M. Henn
Stephen G. Naculich
Howard J. Schnitzer
Marcus Spradlin
Access: Open access
- We extend the analysis of Higgs-regulated planar amplitudes of N = 4 supersymmetric Yang-Mills theory to four loops for the four-gluon amplitude and to two loops for the five-gluon amplitude. Our calculations are consistent with a proposed all-loop ansatz for planar MHV n-gluon amplitudes that is the analog of the BDS ansatz in dimensional regularization. In all cases considered, we have verified that the IR-finite parts of the logarithm of the amplitudes have the same dependence on kinematic variables as the corresponding functions in dimensionally-regulated amplitudes (up to overall additive constants, which we determine). We also study various Regge limits of N = 4 SYM planar n-gluon amplitudes. Euclidean Regge limits of Higgs-regulated n ≥ 4 amplitudes yield results similar in form to those found using dimensional regularization, but with different expressions for the gluon trajectory and Regge vertices resulting from the different regulator scheme. We also show that the Regge limit of the four-gluon amplitude is dominated at next-to-leading-log order by vertical ladder diagrams together with the class of vertical ladder diagrams with a single H-shaped insertion. © 2010 SISSA, Trieste, Italy.
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.
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.
Functional role of gamma and theta oscillations in episodic memory
Date: 2010-06-01
Creator: Erika Nyhus
Tim Curran
Access: Open access
- The primary aim of this review is to examine evidence for a functional role of gamma and theta oscillations in human episodic memory. It is proposed here that gamma and theta oscillations allow for the transient interaction between cortical structures and the hippocampus for the encoding and retrieval of episodic memories as described by the hippocampal memory indexing theory (Teyler and DiScenna, 1986). Gamma rhythms can act in the cortex to bind perceptual features and in the hippocampus to bind the rich perceptual and contextual information from diverse brain regions into episodic representations. Theta oscillations act to temporally order these individual episodic memory representations. Through feedback projections from the hippocampus to the cortex these gamma and theta patterns could cause the reinstatement of the entire episodic memory representation in the cortex. In addition, theta oscillations could allow for top-down control from the frontal cortex to the hippocampus modulating the encoding and retrieval of episodic memories. © 2009.
Do Infant Temperament Characteristics Predict Core Academic Abilities in Preschool-Aged Children?
Date: 2016-01-01
Creator: Maria A. Gartstein
Samuel P. Putnam
Rachel Kliewer
Access: Open access
- Examined relationships between temperament, measured via parent report at 4 months and structured laboratory observations at 12 months of age, and a school readiness battery administered at about 4 years of age (N =31). Scores on the School Readiness Assessment of the Bracken Basic Concept Scale (BBCS) were related to infant Positive Affectivity/Surgency (PAS), with infants described as demonstrating higher levels of PAS at 4 months of age later demonstrating greater school readiness in the domains of color, letter, and number skills. Regulatory Capacity/Orienting (RCO) at 4 months also predicted color skills, with more regulated infants demonstrating superior pre-academic functioning in this area. Analyses involving laboratory observations of temperament provided additional information concerning the importance of infant Positive Affectivity/Surgency, predictive of letter skills and overall school-readiness scores later in childhood. Results are discussed in the context of implications for theory and research, as well as early education settings.