Showing 491 - 500 of 722 Items
Two-loop graviton scattering relation and IR behavior in N = 8 supergravity
Date: 2008-12-11
Creator: Stephen G. Naculich
Horatiu Nastase
Howard J. Schnitzer
Access: Open access
- We derive an ABDK-like relation between the one- and two-loop four-graviton amplitudes in N = 8 supergravity. Specifically we show that the infrared-divergent part of the two-loop amplitude is one-half the square of the one-loop amplitude, suggesting an exponential structure for IR divergences. The difference between the two-loop amplitude and one-half the square of the full one-loop amplitude is therefore finite, and expressible in a relatively simple form. We give arguments for generalizations to higher loops and n-point functions, suggesting that the exponential of the full one-loop amplitude may be corrected, to low orders, by only simple finite terms. © 2008 Elsevier B.V. All rights reserved.
Level-rank duality of untwisted and twisted D-branes of the over(so, ̂) (N)K WZW model
Date: 2007-12-24
Creator: Stephen G. Naculich
Benjamin H. Ripman
Access: Open access
- We analyze the level-rank duality of untwisted and ε-twisted D-branes of the over(so, ̂) (N)K WZW model. Untwisted D-branes of over(so, ̂) (N)K are characterized by integrable tensor and spinor representations of over(so, ̂) (N)K. Level-rank duality maps untwisted over(so, ̂) (N)K D-branes corresponding to (equivalence classes of ) tensor representations onto those of over(so, ̂) (K)N. The ε-twisted D-branes of over(so, ̂) (2 n)2 k are characterized by (a subset of ) integrable tensor and spinor representations of over(so, ̂) (2 n - 1)2 k + 1. Level-rank duality maps spinor ε-twisted over(so, ̂) (2 n)2 k D-branes onto those of over(so, ̂) (2 k)2 n. For both untwisted and ε-twisted D-branes, we prove that the spectrum of an open string ending on these D-branes is isomorphic to the spectrum of an open string ending on the level-rank-dual D-branes. © 2007 Elsevier B.V. All rights reserved.
Ploidy variation in fungi: Polyploidy, aneuploidy, and genome evolution
Date: 2017-07-01
Creator: Robert T. Todd
Anja Forche
Anna Selmecki
Access: Open access
- The ability of an organism to replicate and segregate its genome with high fidelity is vital to its survival and for the production of future generations. Errors in either of these steps (replication or segregation) can lead to a change in ploidy or chromosome number. While these drastic genome changes can be detrimental to the organism, resulting in decreased fitness, they can also provide increased fitness during periods of stress. A change in ploidy or chromosome number can fundamentally change how a cell senses and responds to its environment. Here, we discuss current ideas in fungal biology that illuminate how eukaryotic genome size variation can impact the organism at a cellular and evolutionary level. One of the most fascinating observations from the past 2 decades of research is that some fungi have evolved the ability to tolerate large genome size changes and generate vast genomic heterogeneity without undergoing canonical meiosis.
Thompson's group F is 1-counter graph automatic
Date: 2016-05-01
Creator: Murray Elder
Jennifer Taback
Access: Open access
- It is not known whether Thompson's group F is automatic. With the recent extensions of the notion of an automatic group to graph automatic by Kharlampovich, Khoussainov and Miasnikov and then to C-graph automatic by the authors, a compelling question is whether F is graph automatic or C-graph automatic for an appropriate language class C. The extended definitions allow the use of a symbol alphabet for the normal form language, replacing the dependence on generating set. In this paper we construct a 1-counter graph automatic structure for F based on the standard infinite normal form for group elements.
Twisted D-branes of the over(su, ̂) (N)K WZW model and level-rank duality
Date: 2006-10-30
Creator: Stephen G. Naculich
Howard J. Schnitzer
Access: Open access
- We analyze the level-rank duality of ωc-twisted D-branes of over(su, ̂) (N)K (when N and K > 2). When N or K is even, the duality map involves Z2-cominimal equivalence classes of twisted D-branes. We prove the duality of the spectrum of an open string stretched between ωc-twisted D-branes, and ascertain the relation between the charges of level-rank-dual ωc-twisted D-branes. © 2006 Elsevier B.V. All rights reserved.
Erratum: The 'obligate diploid' Candida albicans forms mating-competent haploids (Nature (2013) 494 (55-59) DOI: 10.1038/nature11865)
Date: 2016-02-11
Creator: Meleah A. Hickman
Guisheng Zeng
Anja Forche
Matthew P. Hirakawa
Darren, Abbey
Benjamin D. Harrison
Yan Ming Wang
Ching Hua Su
Richard J. Bennett
Yue Wang
Judith Berman
Access: Open access
C-graph automatic groups
Date: 2014-09-01
Creator: Murray Elder
Jennifer Taback
Access: Open access
- We generalize the notion of a graph automatic group introduced by Kharlampovich, Khoussainov and Miasnikov by replacing the regular languages in their definition with more powerful language classes. For a fixed language class C, we call the resulting groups C-graph automatic. We prove that the class of C-graph automatic groups is closed under change of generating set, direct and free product for certain classes C. We show that for quasi-realtime counter-graph automatic groups where normal forms have length that is linear in the geodesic length, there is an algorithm to compute normal forms (and therefore solve the word problem) in polynomial time. The class of quasi-realtime counter-graph automatic groups includes all Baumslag-Solitar groups, and the free group of countably infinite rank. Context-sensitive-graph automatic groups are shown to be a very large class, which encompasses, for example, groups with unsolvable conjugacy problem, the Grigorchuk group, and Thompson's groups F, T and V. © 2014 Elsevier Inc.
Time-Periodic Solutions of Driven-Damped Trimer Granular Crystals
Date: 2015-01-01
Creator: E. G. Charalampidis
F. Li
C. Chong
J. Yang
P. G., Kevrekidis
Access: Open access
- We consider time-periodic structures of granular crystals consisting of alternate chrome steel (S) and tungsten carbide (W) spherical particles where each unit cell follows the pattern of a 2: 1 trimer: S-W-S. The configuration at the left boundary is driven by a harmonic in-time actuation with given amplitude and frequency while the right one is a fixed wall. Similar to the case of a dimer chain, the combination of dissipation, driving of the boundary, and intrinsic nonlinearity leads to complex dynamics. For fixed driving frequencies in each of the spectral gaps, we find that the nonlinear surface modes and the states dictated by the linear drive collide in a saddle-node bifurcation as the driving amplitude is increased, beyond which the dynamics of the system becomes chaotic. While the bifurcation structure is similar for solutions within the first and second gap, those in the first gap appear to be less robust. We also conduct a continuation in driving frequency, where it is apparent that the nonlinearity of the system results in a complex bifurcation diagram, involving an intricate set of loops of branches, especially within the spectral gap. The theoretical findings are qualitatively corroborated by the experimental full-field visualization of the time-periodic structures.
Fighting for Every Inch of Land: Greed and Grievance in Petition Mobilization in Zhejiang
Date: 2020-07-01
Creator: Christopher Heurlin
Access: Open access
- Despite a proliferation of studies of the micro-level dynamics of protests and petitions against land takings in China, we know very little about how meso-level factors, such as the local economy, influence petitions to Beijing and provincial governments. Drawing upon the economic approach to civil war, this article examines the roles played by grievances and greed in determining the scale of mobilization at the county level in Zhejiang province. Through archival evidence and interviews in Ningbo and Lishui, as well as an original dataset of petitions, this article suggests that both grievances and greed influence petitioning. Mobilization is especially high in Ningbo, where valuable real estate markets have prompted landless farmers to compete with local governments over control of the rents from land. The article proposes the concept of resource value activation as a cognitive mechanism that has contributed to this process of mobilization.
Recent increases in global HFC-23 emissions
Date: 2010-01-01
Creator: S. A. Montzka
L. Kuijpers
M. O. Battle
M. Aydin
K. R., Verhulst
E. S. Saltzman
D. W. Fahey
Access: Open access
- Firn-air and ambient air measurements of CHF3 (HFC- 23) from three excursions to Antarctica between 2001 and 2009 are used to construct a consistent Southern Hemisphere (SH) atmospheric history. The results show atmospheric mixing ratios of HFC-23 continuing to increase through 2008. Mean global emissions derived from this data for 2006-2008 are 13.5 ± 2 Gg/yr (200 ± 30 × 1012gCO2- equivalent/yr, or MtCO2-eq./yr), ∼50% higher than the 8.7 ± 1 Gg/yr (130 ± 15 MtCO2-eq./yr) derived for the 1990s. HFC-23 emissions arise primarily from over-fluorination of chloroform during HCFC-22 production. The recent global emission increases are attributed to rapidly increasing HCFC-22 production in developing countries since reported HFC-23 emissions from developed countries decreased over this period. The emissions inferred here for developing countries during 2006-2008 averaged 11 ± 2 Gg/yr HFC-23 (160 ± 30 MtCO2-eq./yr) and are larger than the ∼6 Gg/yr of HFC-23 destroyed in United Nations Framework Convention on Climate Change Clean Development Mechanism projects during 2007 and 2008. © Copyright 2010 by the American Geophysical Union.