10,691 research outputs found
The politics of evidence-based policy in Europe’s ‘migration crisis’
Significant increases in the number of refugees and other migrants arriving across the Mediterranean to Europe during 2015 were associated with an increased emphasis on gathering research evidence to enable policymakers to better understand the complexities of migration and improve the policy response. In the UK, the emphasis on evidence-based policy was reflected in funding by the Economic and Social Research Council for a Mediterranean Migration Research Programme. Drawing on the evidence gathered through this programme, the articles in the volume explore the nature of Europe’s ‘migration crisis’ and the extent to which the development of new migration management policies was grounded in evidence about the causes, drivers and consequences of migration to Europe. The authors conclude that there is a substantial ‘gap’ between the now significant body of evidence examining migration processes and European Union policy responses. This gap can be attributed to three main factors: the long-standing ‘paradigm war’ in social research between positivist, interpretivist and critical approaches which means that what counts as ‘evidence’ is contested; competing knowledge claims associated with research and other forms of evidence including the management data to construct and/or support particular policy narratives; and, perhaps most importantly, the political context within which migration policymaking takes place. The politics of policymaking, perhaps nowhere more evident than in the area of migration, has resulted in policies based on underlying assumptions and vested political interests rather than the evidence, even where this evidence has been funded directly by European governments
The Effect of Vitamin Deficiency on Blood Pressure in Rats
After devising a very delicate, modified recording mercury manometer, it was found possible to obtain direct blood pressure curves from the abdominal aorta of anaesthetised rats, previously fed upon specific normal and vitamin deficient diets and thus make comparisons. About 75 animals were used, one-half of this number being normals to check about equally against A and B deficient animals. The records from 22 normals, on growing rations, showed an average of 84 mm. Hg, with the exception of one extremely high and one extremely low figure. The majority were close to the general average. This figure is strikingly close to the figure cited by Uhlmann, where he found the normal pressure in rabbits to be about 90 mm. Hg
String Theory in the Penrose Limit of AdS_2 x S^2
The string theory in the Penrose limit of AdS_2 x S^2 is investigated. The
specific Penrose limit is the background known as the Nappi-Witten spacetime,
which is a plane-wave background with an axion field. The string theory on it
is given as the Wess-Zumino-Novikov-Witten (WZNW) model on non-semi-simple
group H_4. It is found that, in the past literature, an important type of
irreducible representations of the corresponding algebra, h_4, were missed. We
present this "new" representations, which have the type of continuous series
representations. All the three types of representations of the previous
literature can be obtained from the "new" representations by setting the
momenta in the theory to special values. Then we realized the affine currents
of the WZNW model in terms of four bosonic free fields and constructed the
spectrum of the theory by acting the negative frequency modes of free fields on
the ground level states in the h_4 continuous series representation. The
spectrum is shown to be free of ghosts, after the Virasoro constraints are
satisfied. In particular we argued that there is no need for constraining one
of the longitudinal momenta to have unitarity. The tachyon vertex operator,
that correspond to a particular state in the ground level of the string
spectrum, is constructed. The operator products of the vertex operator with the
currents and the energy-momentum tensor are shown to have the correct forms,
with the correct conformal weight of the vertex operator.Comment: 30 pages, Latex, no figure
Spin-charge separation and localization in one-dimension
We report on measurements of quantum many-body modes in ballistic wires and
their dependence on Coulomb interactions, obtained from tunneling between two
parallel wires in a GaAs/AlGaAs heterostructure while varying electron density.
We observe two spin modes and one charge mode of the coupled wires, and map the
dispersion velocities of the modes down to a critical density, at which
spontaneous localization is observed. Theoretical calculations of the charge
velocity agree well with the data, although they also predict an additional
charge mode that is not observed. The measured spin velocity is found to be
smaller than theoretically predicted.Comment: There are minor textual differences between this version and the
version that has been published in Science (follow the DOI link below to
obtain it). In addition, here we have had to reduce figure quality to save
space on the serve
Localization Transition in a Ballistic Quantum Wire
The many-body wave-function of an interacting one-dimensional electron system
is probed, focusing on the low-density, strong interaction regime. The
properties of the wave-function are determined using tunneling between two
long, clean, parallel quantum wires in a GaAs/AlGaAs heterostructure, allowing
for gate-controlled electron density. As electron density is lowered to a
critical value the many-body state abruptly changes from an extended state with
a well-defined momentum to a localized state with a wide range of momentum
components. The signature of the localized states appears as discrete tunneling
features at resonant gate-voltages, corresponding to the depletion of single
electrons and showing Coulomb-blockade behavior. Typically 5-10 such features
appear, where the one-electron state has a single-lobed momentum distribution,
and the few-electron states have double-lobed distributions with peaks at . A theoretical model suggests that for a small number of particles (N<6),
the observed state is a mixture of ground and thermally excited spin states.Comment: 10 pages, 4 figures, 1 tabl
Effect on meteor flight of cooling by radiation and ablation
Evaluation of meteor flight parameters taking into account surface radiation and vapor ablatio
- …