20,333 research outputs found
The Peculiar Velocities of Local Type Ia Supernovae and their Impact on Cosmology
We quantify the effect of supernova Type Ia peculiar velocities on the
derivation of cosmological parameters. The published distant and local Ia SNe
used for the Supernova Legacy Survey first-year cosmology report form the
sample for this study. While previous work has assumed that the local SNe are
at rest in the CMB frame (the No Flow assumption), we test this assumption by
applying peculiar velocity corrections to the local SNe using three different
flow models. The models are based on the IRAS PSCz galaxy redshift survey, have
varying beta = Omega_m^0.6/b, and reproduce the Local Group motion in the CMB
frame. These datasets are then fit for w, Omega_m, and Omega_Lambda using
flatness or LambdaCDM and a BAO prior. The chi^2 statistic is used to examine
the effect of the velocity corrections on the quality of the fits. The most
favored model is the beta=0.5 model, which produces a fit significantly better
than the No Flow assumption, consistent with previous peculiar velocity
studies. By comparing the No Flow assumption with the favored models we derive
the largest potential systematic error in w caused by ignoring peculiar
velocities to be Delta w = +0.04. For Omega_Lambda, the potential error is
Delta Omega_Lambda = -0.04 and for Omega_m, the potential error is Delta
Omega_m < +0.01. The favored flow model (beta=0.5) produces the following
cosmological parameters: w = -1.08 (+0.09,-0.08), Omega_m = 0.27 (+0.02,-0.02)
assuming a flat cosmology, and Omega_Lambda = 0.80 (+0.08,-0.07) and Omega_m =
0.27 (+0.02,-0.02) for a w = -1 (LambdaCDM) cosmology.Comment: 4 pages, 2 figures, 1 table, accepted for publication in ApJ Letter
Does poverty cause conflict? Isolating the causal origins of the conflict trap
Does poverty cause civil conflict? A considerable literature seeks to answer this question, yet concerns about reverse causality threaten the validity of extant conclusions. To estimate the impact of poverty on conflict and to determine whether the relationship between them is causal, it is necessary to identify a source of exogenous variation in poverty. We do this by introducing a robust instrument for poverty: a time-varying measure of international inequalities. We draw upon existing theories about the structural position of a country in the international economic networkāspecifically, the expectation that countries in the core tend to be wealthier and those on the periphery struggle to develop. This instrument is plausibly exogenous and satisfies the exclusion restriction, which suggests that it affects conflict only through its influence upon poverty. Instrumental variables probit regression is employed to demonstrate that the impact of poverty upon conflict appears to be causal
Scorodite precipitation in the presence of antimony
publisher: Elsevier articletitle: Scorodite precipitation in the presence of antimony journaltitle: Chemical Geology articlelink: http://dx.doi.org/10.1016/j.chemgeo.2015.04.013 content_type: article copyright: Copyright Ā© 2015 The Authors. Published by Elsevier B.V.Ā© 2015 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license. The attached file is the published version of the article
The therapeutic potential of allosteric ligands for free fatty acid sensitive GPCRs
G protein coupled receptors (GPCRs) are the most historically successful therapeutic targets. Despite this success there are many important aspects of GPCR pharmacology and function that have yet to be exploited to their full therapeutic potential. One in particular that has been gaining attention in recent times is that of GPCR ligands that bind to allosteric sites on the receptor distinct from the orthosteric site of the endogenous ligand. As therapeutics, allosteric ligands possess many theoretical advantages over their orthosteric counterparts, including more complex modes of action, improved safety, more physiologically appropriate responses, better target selectivity, and reduced likelihood of desensitisation and tachyphylaxis. Despite these advantages, the development of allosteric ligands is often difficult from a medicinal chemistry standpoint due to the more complex challenge of identifying allosteric leads and their often flat or confusing SAR. The present review will consider the advantages and challenges associated with allosteric GPCR ligands, and examine how the particular properties of these ligands may be exploited to uncover the therapeutic potential for free fatty acid sensitive GPCRs
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