22,054 research outputs found
The diversity of quasars unified by accretion and orientation
Quasars are rapidly accreting supermassive black holes at the center of
massive galaxies. They display a broad range of properties across all
wavelengths, reflecting the diversity in the physical conditions of the regions
close to the central engine. These properties, however, are not random, but
form well-defined trends. The dominant trend is known as Eigenvector 1, where
many properties correlate with the strength of optical iron and [OIII]
emission. The main physical driver of Eigenvector 1 has long been suspected to
be the quasar luminosity normalized by the mass of the hole (the Eddington
ratio), an important quantity of the black hole accretion process. But a
definitive proof has been missing. Here we report an analysis of archival data
that reveals that Eddington ratio indeed drives Eigenvector 1. We also find
that orientation plays a significant role in determining the observed
kinematics of the gas, implying a flattened, disklike geometry for the
fast-moving clouds close to the hole. Our results show that most of the
diversity of quasar phenomenology can be unified with two simple quantities,
Eddington ratio and orientation.Comment: This is the author's version of the work; 18 pages including
Supplementary Information; to appear in the 11 September 2014 issue of Nature
at http://dx.doi.org/10.1038/nature1371
Aging vs crystallisation dynamics in hyperquenched glasses and a resolution of the water Tg controversy
The possibility of observing a glass transition in water before
crystallisation occurs has been debated vigorously but inconclusively over five
decades [1,2]. For two decades a glass transition at 136K [2,3] was accepted
but this transition has perplexing qualities [4]. Recently it has been
argued[2,5],that this assignment must be wrong. The re-assignment of Tg to
temperatures above the 150K crystallisation was vigorously contested [6]. Here
we use detailed anneal-and-scan studies of a hyperquenched inorganic glass,
which does not crystallize on heating, to interpret the perplexing aspects of
the 136K water phenomenon. We show that it is indeed linked to a glass
transition, though only via a cross-over phenomenon. The thermal history that
gives the same behaviour ("shadow" glass transition) in the inorganic glass is
linked by crossover to a "normal" glass transition 23% higher in temperature.
Thus a Tg is indeed unobservable for water, while the vitreous nature of
hyperquenched glassy water is strongly supported. The shadow Tg is reproducible
in the inorganic glass as it is in H2O. The observed aging dynamics are very
relevant to current glass theory, particularly to dynamical heterogeneity which
is seen to have an energy manifestation.Comment: 23 pages, 4 figure
The Tariff Equivalent and Forgone Trade Effects of Prohibitive Technical Barriers to Trade
We derive a method to econometrically estimate the tariff equivalent and foregone trade effects of a prohibitive technical barrier to trade (TBT) based on Wales and Woodland's Kuhn-Tucker approach to corner solutions in consumer choice. The method overcomes the lack of observed data on bilateral trade flows and accounts for differentiated goods by place of origin. We apply the derived random utility model to international trade in apples to identify the tariff equivalent of prohibitive nontariff trade barriers imposed by Australia on potential imports of New Zealand apples. We estimate the forgone apple trade between the two countries, the implied trade injury imposed by Australia on New Zealand, and the welfare loss to Australia. The removal of the TBTs would induce net welfare gains around US$50 million annually for Australia.Corner solution; Kuhn-Tucker model; New Zealand apples; nontariff barrier; NTB; prohibitive; random utility; TBT; technical barrier to trade; SPS; phytosanitary
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