oalib

Publish in OALib Journal

ISSN: 2333-9721

APC: Only $99

Submit

Any time

2019 ( 45 )

2018 ( 48 )

2017 ( 59 )

2016 ( 83 )

Custom range...

Search Results: 1 - 10 of 21718 matches for " James Cook "
All listed articles are free for downloading (OA Articles)
Page 1 /21718
Display every page Item
Gauged Wess-Zumino Model in Noncommutative Minkowski Superspace
James S. Cook
Mathematics , 2005, DOI: 10.1063/1.2162330
Abstract: We develop a gauged Wess-Zumino model in noncommutative Minkowski superspace. This is the natural extension of the work of Carlson and Nazaryan, which extended N=1/2 supersymmetry written over deformed Euclidean superspace to Minkowski superspace. We investigate the interaction of the vector and chiral superfields. Noncommutativity is implemented by replacing products with star products. Although, in general, our star product is nonassociative, we prove that it is associative to the first order in the deformation parameter. We show that our model reproduces the N=1/2 theory in the appropriate limit. Essentially, we find the N=1/2 theory and a conjugate copy. As in the N=1/2 theory, a reparameterization of the gauge parameter, vector superfield and chiral superfield are necessary to write standard C-independent gauge theory. However, our choice of parameterization differs from that used in the N=1/2 supersymmetry, which leads to some unexpected new terms.
Infinite dimensional super Lie groups
James Cook,Ronald Fulp
Mathematics , 2006, DOI: 10.1016/j.difgeo.2008.04.009
Abstract: A super Lie group is a group whose operations are $G^{\infty}$ mappings in the sense of Rogers. Thus the underlying supermanifold possesses an atlas whose transition functions are $G^{\infty}$ functions. Moreover the images of our charts are open subsets of a graded infinite-dimensional Banach space since our space of supernumbers is a Banach Grassmann algebra with a countably infinite set of generators. In this context, we prove that if $\hfrak$ is a closed, split sub-super Lie algebra of the super Lie algebra of a super Lie group $\Gcal,$ then $\hfrak$ is the super Lie algebra of a sub-super Lie group of $\Gcal.$ Additionally, we show that if $\gfrak$ is a Banach super Lie algebra satisfying certain natural conditions, then there is a super Lie group $\Gcal$ such that the even part of $\gfrak$ is the even part of the super Lie algebra of $\Gcal.$ In general, the module structure on $\gfrak$ is required to obtain $\Gcal,$ but the "structure constants" involving the odd part of $\gfrak$ can not be recovered without further restrictions. We also show that if $\Hcal$ is a closed sub-super Lie group of a super Lie group $\Gcal,$ then $\Gcal \rar \Gcal/\Hcal$ is a principal fiber bundle. Finally, we show that if $\gfrak$ is a graded Lie algebra over $C,$ then there is a super Lie group whose super Lie algebra is the Grassmann shell of $\gfrak.$ We also briefly relate our theory to techniques used in the physics literature.
Effects of a sex-ratio distorting endosymbiont on mtDNA variation in a global insect pest
Ana M Delgado, James M Cook
BMC Evolutionary Biology , 2009, DOI: 10.1186/1471-2148-9-49
Abstract: The mtDNA phylogeny of 95 individuals sampled from 10 countries on four continents revealed two major clades. One contained only Wolbachia-infected individuals from Malaysia and Kenya, while the other contained only uninfected individuals, from all countries including Malaysia and Kenya. Within the uninfected group was a further clade containing all individuals from Australasia and displaying very limited sequence variation. In contrast, a biparental nuclear gene phylogeny did not have infected and uninfected clades, supporting the notion that maternally-inherited Wolbachia are responsible for the mtDNA pattern. Only about 5% (15/306) of our global sample of individuals was infected with the plutWB1 isolate and even within infected local populations, many insects were uninfected. Comparisons of infected and uninfected isofemale lines revealed that plutWB1 is associated with sex ratio distortion. Uninfected lines have a 1:1 sex ratio, while infected ones show a 2:1 female bias.The main correlate of mtDNA variation in P. xylostella is presence or absence of the plutWB1 infection. This is associated with substantial sex ratio distortion and the underlying mechanisms deserve further study. In contrast, geographic origin is a poor predictor of moth mtDNA sequences, reflecting human activity in moving the insects around the globe. The exception is a clade of Australasian individuals, which may reflect a bottleneck during their recent introduction to this region.Patterns of within-species variation in animal mtDNA are influenced by various factors, including mutation, selection, demography and geography, and analysis of haplotype diversity patterns can provide information on population structure and gene flow. In addition, mtDNA sequences are often used to investigate the evolutionary history of a species, by combining geographic and phylogenetic information in phylogeographic studies [1]. However, theory predicts that mtDNA variation and evolution may also be influenced s
Guggulsterone-Mediated Enhancement of Radiosensitivity in Human Tumor Cell Lines
James B. Mitchell,John A. Cook
Frontiers in Oncology , 2011, DOI: 10.3389/fonc.2011.00019
Abstract: Purpose: To observe the effect of guggulsterone (GS) on the radiation response in human cancer cell lines. Materials and methods: The radiation response of cancer cells treated with GS was observed by cell survival studies, cell growth assay, NF-κB activity assay, western blotting of some key growth promoting receptors, the DNA repair protein γH2AX, and flow cytometry for DNA analyses. Results: GS inhibited radiation induced NF-κB activation and enhanced radiosensitivity in the pancreatic cell line, PC-Sw. It reduced both cell cycle movement and cell growth. GS reduced ERα protein in MCF7 cells and IGF1-Rβ protein in colon cancer cells and pancreatic cancer cells and inhibited DNA double strand break (DSB) repair following radiation. Conclusion: GS induced radiation sensitization may be due to several different mechanisms including the inhibition of NF-κB activation and reductions in IGF1-Rβ. In addition, GS induced γH2AX formation, primarily in the S-phase, indicates that DNA DSB’s in the S-phase may be another reason for GS induced radiosensitivity. ERα down-regulation in response to GS suggests that it can be of potential use in the treatment of estrogen positive tumors that are resistant to tamoxifen.
Torsion points on elliptic curves with complex multiplication
Pete L. Clark,Brian Cook,James Stankewicz
Mathematics , 2009,
Abstract: We present seven theorems on the structure of prime order torsion points on CM elliptic curves defined over number fields. The first three results refine bounds of Silverberg and Prasad-Yogananda by taking into account the class number of the CM order and the splitting of the prime in the CM field. In many cases we can show that our refined bounds are optimal or asymptotically optimal. We also derive asymptotic upper and lower bounds on the least degree of a CM-point on X_1(N). Upon comparison to bounds for the least degree for which there exist infinitely many rational points on X_1(N), we deduce that, for sufficiently large N, X_1(N) will have a rational CM point of degree smaller than the degrees of at least all but finitely many non-CM points.
Investor Na?veté and Asset Prices  [PDF]
Jonathan Cook
Journal of Mathematical Finance (JMF) , 2013, DOI: 10.4236/jmf.2013.34047
Abstract:

This paper describes strategic behavior in a nonequilibrium model of asset pricing with heterogeneous sophistication. Both risk and return are increasing in the na?veté of investors in the market. Optimal investment involves in considering the effect that na?e investors have on the market. Further, we derive a simple characterization of the asset price dynamics that results from an arbitrary combination of a countably infinite set of investor types.

Mechanisms of Esophago-Pharyngeal Acid Regurgitation in Human Subjects
Michal Marcin Szczesniak,Rohan Benjamin Williams,Ian James Cook
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0022630
Abstract: Esophago-pharyngeal regurgitation is implicated in various otolaryngologic and respiratory disorders. The pathophysiological mechanisms causing regurgitation are still largely unknown.
Ant Larval Demand Reduces Aphid Colony Growth Rates in an Ant-Aphid Interaction
Tom H. Oliver,Simon R. Leather,James M. Cook
Insects , 2012, DOI: 10.3390/insects3010120
Abstract: Ants often form mutualistic interactions with aphids, soliciting honeydew in return for protective services. Under certain circumstances, however, ants will prey upon aphids. In addition, in the presence of ants aphids may increase the quantity or quality of honeydew produced, which is costly. Through these mechanisms, ant attendance can reduce aphid colony growth rates. However, it is unknown whether demand from within the ant colony can affect the ant-aphid interaction. In a factorial experiment, we tested whether the presence of larvae in Lasius niger ant colonies affected the growth rate of Aphis fabae colonies. Other explanatory variables tested were the origin of ant colonies (two separate colonies were used) and previous diet (sugar only or sugar and protein). We found that the presence of larvae in the ant colony significantly reduced the growth rate of aphid colonies. Previous diet and colony origin did not affect aphid colony growth rates. Our results suggest that ant colonies balance the flow of two separate resources from aphid colonies- renewable sugars or a protein-rich meal, depending on demand from ant larvae within the nest. Aphid payoffs from the ant-aphid interaction may change on a seasonal basis, as the demand from larvae within the ant colony waxes and wanes.
Deep mtDNA divergences indicate cryptic species in a fig-pollinating wasp
Eleanor R Haine, Joanne Martin, James M Cook
BMC Evolutionary Biology , 2006, DOI: 10.1186/1471-2148-6-83
Abstract: We studied variation in 71 fig-pollinating wasps from across the large geographic range of Ficus rubiginosa in Australia. All wasps sampled belong to one morphological species (Pleistodontes imperialis), but we found four deep mtDNA clades that differed from each other by 9–17% nucleotides. As these genetic distances exceed those normally found within species and overlap those (10–26%) found between morphologically distinct Pleistodontes species, they strongly suggest cryptic fig wasp species. mtDNA clade diversity declines from all four present in Northern Queensland to just one in Sydney, near the southern range limit. However, at most sites multiple clades coexist and can be found in the same tree or even the same fig fruit and there is no evidence for parallel sub-division of the host fig species. Both mtDNA data and sequences from two nuclear genes support the monophyly of the "P. imperialis complex" relative to other Pleistodontes species, suggesting that fig wasp divergence has occurred without any host plant shift. Wasps in clade 3 were infected by a single strain (W1) of Wolbachia bacteria, while those in other clades carried a double infection (W2+W3) of two other strains.Our study indicates that cryptic fig-pollinating wasp species have developed on a single host plant species, without the involvement of host plant shifts, or parallel host plant divergence. Despite extensive evidence for coevolution between figs and fig wasps, wasp speciation may not always be linked strongly with fig speciation.Hosts and their symbionts often have major effects on each other's evolution. Indeed, many symbioses show coevolution of key traits, such as parasite virulence and host resistance and, in some cases, may also manifest cospeciation. A classic example of a coevolved mutualism is provided by the obligate relationship between fig trees (Ficus species) and fig-pollinating wasps (Hymenoptera:Agaonidae). Female wasps enter receptive fig syconia (inflorescences) via a nar
Spatial Stratification of Internally and Externally Non-Pollinating Fig Wasps and Their Effects on Pollinator and Seed Abundance in Ficus burkei
Sarah Al-Beidh,Derek W. Dunn,James M. Cook
ISRN Zoology , 2012, DOI: 10.5402/2012/908560
Abstract: Fig trees (Ficus spp.) are pollinated by tiny wasps that enter their enclosed inflorescences (syconia). The wasp larvae also consume some fig ovules, which negatively affects seed production. Within syconia, pollinator larvae mature mostly in the inner ovules whereas seeds develop mostly in outer ovules—a stratification pattern that enables mutualism persistence. Pollinators may prefer inner ovules because they provide enemy-free space from externally ovipositing parasitic wasps. In some Australasian Ficus, this results in spatial segregation of pollinator and parasite offspring within syconia, with parasites occurring in shorter ovules than pollinators. Australian figs lack non-pollinating fig wasps (NPFW) that enter syconia to oviposit, but these occur in Africa and Asia, and may affect mutualist reproduction via parasitism or seed predation. We studied the African fig, F. burkei, and found a similar general spatial pattern of pollinators and NPFWs within syconia as in Australasian figs. However, larvae of the NPFW Philocaenus barbarus, which enters syconia, occurred in inner ovules. Philocaenus barbarus reduced pollinator abundance but not seed production, because its larvae replaced pollinators in their favoured inner ovules. Our data support a widespread role for NPFWs in contributing to factors preventing host overexploitation in fig-pollinator mutualisms. 1. Introduction Mutualisms are reciprocally beneficial interspecific interactions [1, 2], and a well-known system is that between fig trees (Ficus spp.) and their agaonid wasp pollinators [3–6]. In return for pollination, the wasps gall some fig ovules, which are then eaten by the larvae. About half (300+) of Ficus species are monoecious, where both male flowers and ovules are present in the same syconium (enclosed inflorescence or “fig”). Within monoecious syconia, ovules are highly variable in length [7–10]. Long (inner) ovules have short styles and mature near the centre of the syconium, whereas short (outer), long-styled ovules mature nearer the outer wall (see Figure 1). Female pollinating wasps (foundresses) lay their eggs by inserting their ovipositors down the flower styles. At maturation, wasp galls are clustered at the syconium’s centre [4, 6, 9–13] with seeds at the outer wall. This spatial stratification of pollinating wasps and seeds enables mutualism stability, although the mechanisms preventing the wasps from galling all ovules are unclear. Figure 1: Variation in style and pedicel length in female flowers of monoecious Ficus (adapted from Dunn et al. [ 13]). Mechanisms proposed to
Page 1 /21718
Display every page Item


Home
Copyright © 2008-2017 Open Access Library. All rights reserved.