Showing 691 - 700 of 2039 Items
Are melanized feather barbs stronger?
Date: 2004-01-01
Creator: Michael Butler
Amy S. Johnson
Access: Open access
- Melanin has been associated with increased resistance to abrasion, decreased wear and lowered barb breakage in feathers. But, this association was inferred without considering barb position along the rachis as a potentially confounding variable. We examined the cross-sectional area, breaking force, breaking stress, breaking strain and toughness of melanized and unmelanized barbs along the entire rachis of a primary feather from an osprey (Pandion haliaetus). Although breaking force was higher for melanized barbs, breaking stress (force divided by cross-sectional area) was greater for unmelanized barbs. But when position was considered, all mechanical differences between melanized and unmelanized barbs disappeared. Barb breaking stress, breaking strain and toughness decreased, and breaking stiffness increased, distally along the rachis. These proximal-distal material property changes are small and seem unlikely to affect flight performance of barbs. Our observations of barb bending, breaking and morphology, however, lead us to propose a design principle for barbs. We propose that, by being thicker-walled dorso-ventrally, the barb's flexural stiffness is increased during flight; but, by allowing for twisting when loaded with dangerously high forces, barbs firstly avoid failure by bending and secondly avoid complete failure by buckling rather than rupturing.
Linear relations between N ≥ 4 supergravity and subleading-color SYM amplitudes
Date: 2012-02-27
Creator: Stephen G. Naculich
Horatiu Nastase
Howard J. Schnitzer
Access: Open access
- The IR divergences of supergravity amplitudes are less severe than those of planar SYM amplitudes, and are comparable to those subleading-color SYM amplitudes that are most subleading in the 1/N expansion, namely O(1/ε L) for L-loop amplitudes. We derive linear relations between one- and two-loop four-point amplitudes and one-loop five-point amplitudes of N ≥ 4, 5, and 6 supergravity and the most-subleading-color contributions of the analogous amplitudes of N = 0, 1, and 2 SYM theory, extending earlier results for N = 8 supergravity amplitudes. Our work relies on linear relations between N = 4 supergravity and planar SYM amplitudes that were recently derived using the double-copy property of gravity, and color-kinematic duality of gauge theories. © SISSA 2012.
Interest groups in electoral politics: 2012 in context
Date: 2012-12-01
Creator: Michael M. Franz
Access: Open access
- This paper compares the levels of ad spending from outside groups and traditional party organizations across seven federal election cycles. The data show clearly that outside groups advertised at historic levels in 2012. Such intense efforts send two important signals to students of American campaign finance. The first involves a crisis in the system of limited donations to candidates and party committees moving forward. The second resurrects an old debate in political science about whether parties or candidates should be the center of our electoral process. The paper concludes with a consideration of possible reforms that might help restore parties and candidates to the center of issue debates in competitive federal elections.
Peatlands and their role in the global carbon cycle
Date: 2011-04-20
Creator: Zicheng Yu
D. W. Beilman
S. Frolking
G. M. MacDonald
N. T., Roulet
P. Camill
D. J. Charman
Access: Open access
- Global peatlands store a very large carbon (C) pool located within a few meters of the atmosphere. Thus, peatland-atmosphere C exchange should be a major concern to global change scientists: Will large amounts of respired belowground C be released in a warmer climate, causing the climate to further warm (a positive climate feedback)? Will more C be sequestered due to increased plant growth in a warmer climate? How will land use change, fires, and permafrost thaw affect the magnitude and direction of carbon dioxide (CO ) and methane (CH ) exchange with the atmosphere? These questions remain challenging, but some significant progress has been made recently. 2 4
Lipschitzian multifunctions and a Lipschitzian inverse mapping theorem
Date: 2001-01-01
Creator: A.B. Levy
Access: Open access
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.