14,635 research outputs found
Attentional avoidance of high-fat food in unsuccessful dieters
Using the exogenous cueing task, this study examined whether restrained and disinhibited eaters differ in their orientation of attention towards and their difficulty to disengage from high versus low-fat food pictures in a relatively short (500 ms) and a long presentation format (1500 ms). Overall, participants in the 500 ms condition showed a tendency to direct attention away from high-fat food pictures compared to neutral pictures. No differential pattern was evident for the 1500 ms condition. Correlational analysis revealed that reduced engagement with high-fat food was particularly pronounced for disinhibited eaters. Although in the short term this seems an adaptive strategy, it may eventually become counterproductive, as it could hinder habituation and learning to cope with seductive characteristics of high-fat food. (C) 2010 Elsevier Ltd. All rights reserved
QuantMig:The use of migration scenarios in future characterisations: A systematic review and typology
BackgroundMigration plays an increasingly important role in shaping the demographic profiles of developed countries and receives ample attention in society at large as well as among policymakers. To understand how migration flows might evolve in the future, the QuantMig project set the goal of producing migration scenarios to support European migration policy. To do so, we need to make clear with what purpose scenarios are developed, how they are developed, and on which flows they focus. Other questions concern whether they are designed to describe the most likely future or a possible future, whether they are extrapolating trends observed in the past (assuming no fundamental changes in policies), or whether they are designed to describe desirable futures (migration as a panacea for ageing societies) or undesirable futures (massive inflow of immigration from developing countries). To produce the best possible migration scenarios, it is essential to get an overview of the literature. Migration scenarios have been used in a variety of future characterisations including forecasts, projections, and foresights. However, the term migration scenario is rarely well-defined or used consistently. Before developing a set of own scenarios, this document takes the necessary step of providing an overview of the existing literature and provide a definition and typology of migration scenarios. Based on this work, alternative ways of exploring the future of migration (for example in a vignette survey) will be discussed that lay out the bases for the extension of the work in the next deliverables of the work package. MethodsThis document looks at how migration scenarios are used in the literature presenting characterisations of societies’ futures. Relevant documents are systematically retrieved and assigned to one of six categories part of a pre-established typology. The typology rests on the focus (either migration or another aspect of societies influenced by migration) and purpose (either to predict the future, explore the future, or establish how a specific target can be reached) of each future characterisation. Subsequently, the techniques used for generating migration scenarios are described in terms of the approach taken (quantitative or qualitative) and how data is generated and transformed into meaningful output. Finally, the specific geographical context and characteristics of migration and migrants included in the scenarios are explored. ResultsA total of 107 documents were analysed. More than half presented migration scenarios that were developed to answer questions not about migration itself, but about its influence on a population’s future growth, age composition, or economic performance, among others. Future characterisations had most often prediction as purpose, being for example population forecasts, while many others had exploration as purpose, where the sensitivity of a given phenomenon to different migration assumptions is assessed. Most scenarios rest on a quantitative approach rather than on a narrative, but the latter has clearly expanded in the last years. Migration scenarios that follow a quantitative approach often rest on past migration trends to characterise the future, but seldom provide likelihoods that a given scenario will realise. Migration scenarios that follow a qualitative approach, on the other hand, often rest on experts and stakeholders’ views for input, or rely on previously developed storylines. Finally, quantitative scenarios often concentrate on net migration figures inside of a single, usually economically developed country, while qualitative scenarios are more likely to consider bidirectional flows between two (world) regions. ConclusionsThere was an increase over time in the use of qualitative scenarios to characterise the future of migration. However, these scenarios were seldom used to translate storylines into quantitative outputs that specifically aim at predicting future migration flows. Ways to achieve this are discussed, including more advanced data collection techniques among experts and stakeholders, and the consideration of multiple types of migration
QuantMig:The use of migration scenarios in future characterisations: A systematic review and typology
BackgroundMigration plays an increasingly important role in shaping the demographic profiles of developed countries and receives ample attention in society at large as well as among policymakers. To understand how migration flows might evolve in the future, the QuantMig project set the goal of producing migration scenarios to support European migration policy. To do so, we need to make clear with what purpose scenarios are developed, how they are developed, and on which flows they focus. Other questions concern whether they are designed to describe the most likely future or a possible future, whether they are extrapolating trends observed in the past (assuming no fundamental changes in policies), or whether they are designed to describe desirable futures (migration as a panacea for ageing societies) or undesirable futures (massive inflow of immigration from developing countries). To produce the best possible migration scenarios, it is essential to get an overview of the literature. Migration scenarios have been used in a variety of future characterisations including forecasts, projections, and foresights. However, the term migration scenario is rarely well-defined or used consistently. Before developing a set of own scenarios, this document takes the necessary step of providing an overview of the existing literature and provide a definition and typology of migration scenarios. Based on this work, alternative ways of exploring the future of migration (for example in a vignette survey) will be discussed that lay out the bases for the extension of the work in the next deliverables of the work package. MethodsThis document looks at how migration scenarios are used in the literature presenting characterisations of societies’ futures. Relevant documents are systematically retrieved and assigned to one of six categories part of a pre-established typology. The typology rests on the focus (either migration or another aspect of societies influenced by migration) and purpose (either to predict the future, explore the future, or establish how a specific target can be reached) of each future characterisation. Subsequently, the techniques used for generating migration scenarios are described in terms of the approach taken (quantitative or qualitative) and how data is generated and transformed into meaningful output. Finally, the specific geographical context and characteristics of migration and migrants included in the scenarios are explored. ResultsA total of 107 documents were analysed. More than half presented migration scenarios that were developed to answer questions not about migration itself, but about its influence on a population’s future growth, age composition, or economic performance, among others. Future characterisations had most often prediction as purpose, being for example population forecasts, while many others had exploration as purpose, where the sensitivity of a given phenomenon to different migration assumptions is assessed. Most scenarios rest on a quantitative approach rather than on a narrative, but the latter has clearly expanded in the last years. Migration scenarios that follow a quantitative approach often rest on past migration trends to characterise the future, but seldom provide likelihoods that a given scenario will realise. Migration scenarios that follow a qualitative approach, on the other hand, often rest on experts and stakeholders’ views for input, or rely on previously developed storylines. Finally, quantitative scenarios often concentrate on net migration figures inside of a single, usually economically developed country, while qualitative scenarios are more likely to consider bidirectional flows between two (world) regions. ConclusionsThere was an increase over time in the use of qualitative scenarios to characterise the future of migration. However, these scenarios were seldom used to translate storylines into quantitative outputs that specifically aim at predicting future migration flows. Ways to achieve this are discussed, including more advanced data collection techniques among experts and stakeholders, and the consideration of multiple types of migration
Towards a fully self-consistent spectral function of the nucleon in nuclear matter
We present a calculation of nuclear matter which goes beyond the usual
quasi-particle approximation in that it includes part of the off-shell
dependence of the self-energy in the self-consistent solution of the
single-particle spectrum. The spectral function is separated in contributions
for energies above and below the chemical potential. For holes we approximate
the spectral function for energies below the chemical potential by a
-function at the quasi-particle peak and retain the standard form for
energies above the chemical potential. For particles a similar procedure is
followed. The approximated spectral function is consistently used at all levels
of the calculation. Results for a model calculation are presented, the main
conclusion is that although several observables are affected by the inclusion
of the continuum contributions the physical consistency of the model does not
improve with the improved self-consistency of the solution method. This in
contrast to expectations based on the crucial role of self-consistency in the
proofs of conservation laws.Comment: 26 pages Revtex with 4 figures, submitted to Phys. Rev.
Shot noise in ferromagnet--normal metal systems
A semiclassical theory of the low frequency shot noise in ferromagnet -
normal metal systems is formulated. Non-collinear magnetization directions of
the ferromagnetic leads, arbitrary junctions and the elastic and inelastic
scattering regimes are considered. The shot noise is governed by a set of
mesoscopic parameters that are expressed in terms of the microscopic details of
the junctions in the circuit. Explicit results in the case of ballistic,
tunnel, and diffusive junctions are evaluated. The shot noise, the current and
the Fano factor are calculated for a double barrier ferromagnet - normal metal
- ferromagnet system. It is demonstrated that the shot noise can have a
non-monotonic behavior as a function of the relative angle between the
magnetizations of the ferromagnetic reservoirs.Comment: 17 pages, 7 figure
Reflection of light from a disordered medium backed by a phase-conjugating mirror
This is a theoretical study of the interplay of optical phase-conjugation and
multiple scattering. We calculate the intensity of light reflected by a
phase-conjugating mirror when it is placed behind a disordered medium. We
compare the results of a fully phase-coherent theory with those from the theory
of radiative transfer. Both methods are equivalent if the dwell time
\tau_{dwell} of a photon in the disordered medium is much larger than the
inverse of the frequency shift 2\Delta\omega acquired at the phase-conjugating
mirror. When \tau_{dwell} \Delta\omega < 1, in contrast, phase coherence
drastically affects the reflected intensity. In particular, a minimum in the
dependence of the reflectance on the disorder strength disappears when
\Delta\omega is reduced below 1/\tau_{dwell}. The analogies and differences
with Andreev reflection of electrons at the interface between a normal metal
and a superconductor are discussed.Comment: 27 pages RevTeX with 11 figures included with psfi
Quantum-Statistical Current Correlations in Multi-Lead Chaotic Cavities
Quantum mechanics requires that identical particles are treated as
indistinguishable. This requirement leads to correlations in the fluctuating
properties of a system. Theoretical predictions are made for an experiment on a
multi-lead chaotic quantum dot which can identify exchange effects in
electronic current-current correlations. Interestingly, we find that the
ensemble averaged exchange effects are of the order of the channel number, and
are insensitive to dephasing.Comment: 4 pages REVTEX, including two figure
Star formation in disk galaxies driven by primordial H_2
We show that gaseous \HI disks of primordial composition irradiated by an
external radiation field can develop a multiphase medium with temperatures
between 10^2 and 10^4 K due to the formation of molecular hydrogen. For a given
\HI column density there is a critical value of the radiation field below which
only the cold \HI phase can exist. Due to a time decreasing quasar background,
the gas starts cooling slowly after recombination until the lowest stable
temperature in the warm phase is reached at a critical redshift .
Below this redshift the formation of molecular hydrogen promotes a rapid
transition towards the cold \HI phase. We find that disks of protogalaxies with
10^{20}\simlt N_{HI}\simlt 10^{21} cm^{-2} are gravitationally stable at
K and can start their star formation history only at z \simlt
z_{cr}\sim 2, after the gas in the central portion of the disk has cooled to
temperatures T\simlt 300 K. Such a delayed starbust phase in galaxies of low
gas surface density and low dynamical mass can disrupt the disks and cause them
to fade away. These objects could contribute significantly to the faint blue
galaxy population.Comment: 16 pages (LaTeX), 2 Figures to be published in Astrophysical Journal
Letter
Charge fluctuations in a quantum point contact attached to a superconducting lead
We show how to calculate the charge noise spectrum in a normal mesoscopic
conductor, which is capacitively coupled to a macroscopic gate, when this
conductor is attached to L normal leads and M superconducting leads, the only
restriction being that the superconducting leads must be at the same chemical
potential. We then proceed to examine results for a quantum point contact (QPC)
in a normal lead connecting to a superconductor. Of interest is the fluctuating
current in a gate capacitively coupled to a QPC. The results are compared with
the case when all leads are normal. We find a doubling of the equilibrium
charge fluctuations and a large enhancement (>2) in the current noise spectrum
to first order in |eV|, when a channel in the QPC is opening.Comment: 4 pages, 3 figure
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