321 research outputs found
PP-waves from BPS supergravity monopoles
We discuss the Penrose limit of the Chamseddine-Volkov BPS selfgravitating
monopole in four dimensional N=4 supergravity theory with non-abelian gauge
multiplets. We analyze the properties of the resulting supersymmetric pp-wave
solutions when various Penrose limits are considered. Apart from the usual
rescaling of coordinates and fields we find that a rescaling of the gauge
coupling constant to zero is required, rendering the theory abelian. We also
study the Killing spinor equations showing an enhancement of the
supersymmetries preserved by the solutions and discuss the embedding of the
pp-wave solution in dimensions.Comment: 14 pages, no figures. Minor changes, to appear in Phys. Lett.
On Coordinate Transformations in Planar Noncommutative Theories
We consider planar noncommutative theories such that the coordinates verify a
space-dependent commutation relation. We show that, in some special cases, new
coordinates may be introduced that have a constant commutator, and as a
consequence the construction of Field Theory models may be carried out by an
application of the standard Moyal approach in terms of the new coordinates. We
apply these ideas to the concrete example of a noncommutative plane with a
curved interface. We also show how to extend this method to more general
situations.Comment: 20 pages, 1 figure. references adde
Fire and climate: contrasting pressures on tropical Andean timberline species
Department of Biological Sciences; Florida Institute of Technology; Melbourne FL USA Department of Biological Sciences; Florida Institute of Technology; Melbourne FL USA Department of Biological Sciences; Florida Institute of Technology; Melbourne FL USA Geography, College of Life & Environmental Sciences; University of Exeter; Exeter UK Department of Biological Sciences; Florida Institute of Technology; Melbourne FL USA CEPSAR; The Open University; Milton Keynes UK Instituto de GeologĂa; Universidad Nacional AutĂłnoma de MĂ©xico; Ciudad Universitaria; Mexico City Mexico Department of Forest and Soil Sciences; University of Natural Resources and Life Sciences Vienna; Vienna Austria Department of Biology and Center for Energy; Environment and Sustainability; Wake Forest University; Winston Salem NC USACopyright © 2015 John Wiley & Sons Ltd.Aim: The aim was to test competing hypotheses regarding migration of the Andean timberline within the last 2000 years.
Location: The upper forest limit in Manu National Park, Peru.
Methods: A randomized stratified design provided 21 soil profiles from forested sites just below the timberline, 15 from puna grassland sites just above the timberline and 15 from the transitional habitat at the punaâforest boundary. From each profile a surface sample (hereafter modern) and a sample from the base of the organic horizon (hereafter historical) were collected. Pollen and charcoal were analysed from the modern and historical layers of the 51 soil profiles. A chronological framework was provided by 24 14C dates. Data were ordinated as modern and historical groups and the temporal trends illustrated by Procrustes rotation.
Results: The organic layer from the soil profiles represented the last 600â2000 years. Fire was much more abundant in all habitat types (puna, transitional and forested) in the modern compared with the historical groups. Samples that had historically been in puna just above the timberline showed encroachment by woody species. Samples that had been forested were still classified as forest but their composition had become more transitional. Sites that were transitional appeared to represent a new or expanded class of sites that was far less abundant historically.
Main conclusions: Our results are consistent with ongoing warming causing an upslope migration of species, although not necessarily of the timberline. Weedy fire-tolerant species are spreading upslope, creating a transitional forest, softening the boundary between forest and puna. Simultaneously, fire introduced to improve grazing outside the park has increasingly penetrated the forest and is causing the upper timberline to shift towards more fire-tolerant and weedy species. Consequently, both the form of the ecotone between forest and grassland and the species composition of these forests is changing and is expected to continue to change, representing a shifting baseline for what is considered to be natural.Gordon and Betty Moore Foundation Andes-to-Amazon programmeBlue Moon FundNational Science Foundatio
KK-Masses in Dipole Deformed Field Theories
We reconsider aspects of non-commutative dipole deformations of field
theories. Among our findings there are hints to new phases with spontaneous
breaking of translation invariance (stripe phases), similar to what happens in
Moyal-deformed field theories. Furthermore, using zeta-function regularization,
we calculate quantum corrections to KK-state masses. The corrections coming
from non-planar diagrams show interesting but non-universal behaviour.
Depending on the type of interaction the corrections can make the KK-states
very heavy but also very light or even tachyonic. Finally we point out that the
dipole deformation of QED is not renormalizable!Comment: 21 pages, 5 figures, uses axodraw.sty, JHEP3.cls; v2:revised version
with minor change
Comments on the U(2) Noncommutative Instanton
We discuss the 't Hoof ansatz for instanton solutions in noncommutative U(2)
Yang-Mills theory. We show that the extension of the ansatz leading to singular
solutions in the commutative case, yields to non self-dual (or self-antidual)
configurations in noncommutative space-time. A proposal leading to selfdual
solutions with Q=1 topological charge (the equivalent of the regular BPST
ansatz) can be engineered, but in that case the gauge field and the curvature
are not Hermitian (although the resulting Lagrangian is real).Comment: Latex file, no figure
Comments on Noncommutative ADHM Construction
We extend the method of matrix partition to obtain explicitly the gauge field
for noncommutative ADHM construction in some general cases. As an application
of this method we apply it to the U(2) 2-instanton and get explicit result for
the gauge fields in the coincident instanton limit. We also easily apply it to
the noncommutative 't Hooft instantons in the appendix.Comment: 17 pages, LaTeX; an appendix added, typos corrected, refs adde
Muscle mass to visceral fat ratio is an important predictor of the metabolic syndrome in college students
This study aimed to evaluate the associations between the muscle mass to visceral fat (MVF) ratio and cardiometabolic risk factors in a large population of college students in Colombia and to propose cut-off points of this index for the metabolic syndrome (MetS). A total of 1464 young adults recruited from the FUPRECOL (Asociación de la Fuerza Prensil con Manifestaciones Tempranas de Riesgo Cardiovascular en Jóvenes y Adultos Colombianos) study were categorised into four groups based on their MVF ratio. Muscle mass and visceral fat level of the participants were measured using a bioelectrical impedance analysis. Cardiometabolic risk factors including lifestyle characteristics, anthropometry, blood pressure and biochemical parameters were assessed. The prevalence of moderate to severe obesity, hypertension and the MetS was higher in subjects in quartile (Q)1 (lower MVF ratio) (P less than 0·001). ANCOVA revealed that the subjects in Q1 had higher cardiometabolic disturbances, including altered anthropometry, blood pressure, muscle strength and biochemical parameters after adjusting for age and sex compared with young adults in higher MVF ratio quartiles (P less than 0·001). Muscular mass and physical activity levels were significantly lower in subjects with a lower MVF ratio (P less than 0·001). The receiver operating characteristic curve analyses indicated that in men the best MVF ratio cut-off point for detecting the MetS was 18·0 (AUC 0·83, sensitivity 78 % and specificity 77 %) and for women, the MVF ratio cut-off point was 13·7 (AUC 0·85, sensitivity 76 % and specificity 87 %). A lower MVF ratio is associated with a higher risk cardiometabolic profile in early adulthood, supporting that the MVF ratio could be used as a complementary screening tool that may help clinicians identify young adults at high cardiometabolic risk. © The Authors 2018
Some Noncommutative Multi-instantons from Vortices in Curved Space
We construct U(2) noncommutative multi-instanton solutions by extending
Witten's ansatz [1] which reduces the problem of cylindrical symmetry in four
dimensions to that of a set of Bogomol'nyi equations for an Abelian Higgsmodel
in two dimensional curved space. Using the Fock space approach, we give
explicit vortex solutions to the Bogomol'nyi equations and, from them, we
present multi-instanton solutions.Comment: 10 pages. LaTe
Giant Gravitons - with Strings Attached (III)
We develop techniques to compute the one-loop anomalous dimensions of
operators in the super Yang-Mills theory that are dual to open
strings ending on boundstates of sphere giant gravitons. Our results, which are
applicable to excitations involving an arbitrary number of open strings,
generalize the single string results of hep-th/0701067. The open strings we
consider carry angular momentum on an S embedded in the S of the
AdSS background. The problem of computing the one loop anomalous
dimensions is replaced with the problem of diagonalizing an interacting Cuntz
oscillator Hamiltonian. Our Cuntz oscillator dynamics illustrates how the
Chan-Paton factors for open strings propagating on multiple branes can arise
dynamically.Comment: 66 pages; v2: improved presentatio
Managing the trade-off implications of global supply
The cost versus response trade-off is a growing logistics issue due to many markets being increasingly characterized by demand uncertainty and shorter product life cycles. This is exacerbated further with supply increasingly moving to low cost global sources. However, the poor response implications of global supply are often not addressed or even acknowledged when undertaking such decisions. Consequently, various practical approaches to minimising, postponing or otherwise managing the impact of the demand uncertainty are often only adopted retrospectively. Even though such generic solutions are documented through case examples we lack effective tools and concepts to support the proactive identification and resolution of such trade-offs. This paper reports on case-based theory building research, involving three cases from the UK and USA used in developing a conceptual model with associated tools, in support of such a process
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