14,708 research outputs found
Yangians, Grassmannians and T-duality
We investigate the Yangian symmetry of scattering amplitudes in N=4 super
Yang-Mills theory and show that its formulations in twistor and momentum
twistor space can be interchanged. In particular we show that the full symmetry
can be thought of as the Yangian of the dual superconformal algebra,
annihilating the amplitude with the MHV part factored out. The equivalence of
this picture with the one where the ordinary superconformal symmetry is thought
of as fundamental is an algebraic expression of T-duality. Motivated by this,
we analyse some recently proposed formulas, which reproduce different
contributions to amplitudes through a Grassmannian integral. We prove their
Yangian invariance by directly applying the generators.Comment: 28 pages, 1 figure; v2: minor correction
Fourier Decomposition of RR Lyrae light curves and the SX Phe population in the central region of NGC 3201
CCD time-series observations of the central region of the globular cluster
NGC~3201 were obtained with the aim of performing the Fourier decomposition of
the light curves of the RR~Lyrae stars present in that field. This procedure
gave the mean values, for the metallicity, of [Fe/H]
(statistical) (systematical), and for the distance, ~kpc (statistical) (systematical). The values found from two
RRc stars are consistent with those derived previously. The differential
reddening of the cluster was investigated and individual reddenings for the RR
Lyrae stars were estimated from their curves. We found an average value
of . An investigation of the light curves of stars in
the {\it blue stragglers} region led to the discovery of three new SX~Phe
stars. The period-luminosity relation of the SX~Phe stars was used for an
independent determination of the distance to the cluster and of the individual
reddenings. We found a distance of 5.0 kpcComment: To appear in Revista Mexicana de Astronom\'ia y Astrof\'isica,
Octuber 2014 issue, Vol 50. 17 pages, 10 figure
Physical parameters of three field RR Lyrae stars
This work was partially supported by DGAPA–Universidad Nacional Autonoma de Mexico through project IN104612.Stromgren uvby - beta photometry of the stars classified as RR Lyrae stars RU Piscium, SS Piscium and TU Ursae Majoris has been used to estimate their iron abundance, temperature, gravity and absolute magnitude. The stability of the pulsating period is discussed. The nature of SS Psc as a RRc or a HADS is addressed. The reddening of each star is estimated from the Stromgren colour indices and reddening sky maps. The results of three approaches to the determination of [Fe/H], T-eff and log(g) are discussed: Fourier light curve decomposition, the Preston Delta S index and the theoretical grids on the (b - y)(o) - c(10) plane.Peer reviewe
Historical cohort study examining comparative effectiveness of albuterol inhalers with and without integrated dose counter for patients with asthma or chronic obstructive pulmonary disease
This study was supported financially by an unrestricted grant from Teva Pharmaceuticals, Frazer, PA, USA. The authors thank Jenny Fanstone of Fanstone Medical Communications Ltd., UK, and Elizabeth V Hillyer for medical writing support, funded by Research in Real-Life. We acknowledge with gratitude Dr Ruchir Parikh for his review of and contributions to the manuscript.Peer reviewedPublisher PD
Combating overpopulation : a study of the population policies of China and India
With the world population now at 6 billion, the topic of overpopulation is becoming increasingly important. The planet cannot absorb an infinite number of humans, and steps need to be taken to combat unchecked growth. The thesis begins with a discussion of the problems currently manifesting themselves, including land degradation, water supply loss, farmland appropriation for living space, overfishing, and unequal food distribution. The thesis considers the population policy of China, long criticized by the West for its unusual harshness. In studying its history, though, it can be seen why the Chinese government felt radical steps were necessary. India\u27s policy over the last few decades is also examined. In this case, early excesses on the government\u27s part led to public unpopularity for the whole population control concept. Despite this, positive steps have been taken in several areas. The current availability of food and farmland in both states is studied to determine what environmental and nutritional effects the respective population policies have had. Comparisons are made between the two in an effort to gauge their relative success and to attempt to draw any lessons for either China or India
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