10,680 research outputs found
Pair-transfer probability in open- and closed-shell Sn isotopes
Approximations made to estimate two-nucleon transfer probabilities in
ground-state to ground-state transitions and physical interpretation of these
probabilities are discussed. Probabilities are often calculated by
approximating both ground states, of the initial nucleus A and of the final
nucleus A\pm 2 by the same quasiparticle vacuum. We analyze two improvements of
this approach. First, the effect of using two different ground states with
average numbers of particles A and A\pm2 is quantified. Second, by using
projection techniques, the role of particle number restoration is analyzed. Our
analysis shows that the improved treatment plays a role close to magicity,
leading to an enhancement of the pair-transfer probability. In mid-shell
regions, part of the error made by approximating the initial and final ground
states by a single vacuum is compensated by projecting onto good particle
number. Surface effects are analyzed by using pairing interactions with a
different volume-to-surface mixing. Finally, a simple expression of the
pair-transfer probability is given in terms of occupation probabilities in the
canonical basis. We show that, in the canonical basis formulation, surface
effects which are visible in the transfer probability are related to the
fragmentation of single-particle occupancies close to the Fermi energy. This
provides a complementary interpretation with respect to the standard
quasiparticle representation where surface effects are generated by the
integrated radial profiles of the contributing wave functions.Comment: 12 pages, 7 figure
Voltage induced control and magnetoresistance of noncollinear frustrated magnets
Noncollinear frustrated magnets are proposed as a new class of spintronic
materials with high magnetoresistance which can be controlled with relatively
small applied voltages. It is demonstrated that their magnetic configuration
strongly depends on position of the Fermi energy and applied voltage. The
voltage induced control of noncollinear frustrated materials (VCFM) can be seen
as a way to intrinsic control of colossal magnetoresistance (CMR) and is the
bulk material counterpart of spin transfer torque concept used to control giant
magnetoresistance in layered spin-valve structures.Comment: 4 pages, 4 figure
The effect of metacognitive strategy instruction on L2 learner beliefs and listening skills
This pilot study investigated the effect of semester-long strategy-based instruction on
learner beliefs and skills in the processing of aural input by adult learners of English as a
second language at metacognitive and procedural levels. The study addressed two
frequently encountered learner beliefs thought to impede L2 processing of aural input:
The little words aren’t important; intonation is merely decorative. Working on the
premise that learner beliefs underpin learner strategies for processing aural input and are
reflected in learner productive and receptive skills, pre- and post-instruction instruments
measured both learners’ awareness of connected speech processes and the functions of
intonation, and their ability to segment a continuous speech stream, and to process
utterances for speaker intent. Findings using repeated measures analysis of variance
support strategy-based metacognitive training in connected speech and stress and
intonation to promote listening skills awareness, aid word segmentation, and facilitate
understanding utterance content and intended meaning.Published versio
To what extent would the poorest consumers nutritionally and socially benefit from a global food tax and subsidy reform ? A framed field experiment based on daily food intake
In this paper we propose a new method in experimental economics, designed to evaluate the effectiveness of public policy incentives aimed at altering consumer behaviors. We apply this method to wide-ranging policies on food prices, which use subsidies to increase the consumption of healthy products and taxes to reduce that of unhealthy ones. Our protocol allows for observation of an individual’s daily food consumption before and after the policy. We examine two separate policies: the one subsidizes fruit and vegetables, while the other one combines taxes and subsidies. We measure their nutritional and economic impacts on the choices of low-income French consumers, compared to a reference group. Both policies have a positive effect on the nutritional quality of food choices of the two groups but initial gaps widen, especially with the subsidies. In the low-income group this can be explained by an initially unfavorable pattern and by weaker price elasticities. The redistributive effects are therefore doubly regressive. Moreover, the individual price elasticities, that the experimental approach enables us to measure, show widely diverse behaviors. They are counter-effective for close to 40% of our sample of poor women.OBESITY;PUBLIC POLICY;SOCIAL INEQUALITIES;POVERTY;INCOME REDISTRIBUTION;REGRESSIVE TAX;INDIVIDUALIZED PRICE INDEX;NUTRITIONAL TAX SYSTEM;FOOD TAX
Interest of site-specific pollution control policies
Owing to increasing environmental concerns the current trend is to bend technical production systems in order to adapt them to the specific characteristics of the milieu and diversify them. Inherent to such dynamics is the issue of how to design the accompanying environmental policies. Theoretically, spatially targeted environmental policies are considered optimal, since economic agents tune their efforts according to the sensitivity of the milieu where they operate. But, according to empirical analyses, this advantage is undermined by the high cost of implementation, monitoring and enforcement. This paper outlines the conditions required for site-specific policies to be effective at least cost. Our starting point is the nitrate pollution of water from agriculture, which varies according to climate, soil type and agricultural production system. Farm management practices enabling to reduce pollution depend on this variability. An interdisciplinary study of the efficiency of differentiating the way this pollution is regulated was carried out on two sites in France. It focussed on assessing the importance of spatial variability in physical parameters and in private and social costs.NONPOINT POLLUTION; SITE SPECIFIC TECHNOLOGY; SITE SPECIFIC ENVIRONMENTAL POLICY; ABATEMENT COST; TRANSACTION COST
s- and d-wave superconductivity in a two-band model
Superconductivity in strongly correlated systems is a remarkable phenomenon
that attracts a huge interest. The study of this problem is relevant for
materials as the high Tc oxides, pnictides and heavy fermions. In this work we
study a realistic model that includes the relevant physics of superconductivity
in the presence of strong Coulomb correlations. We consider a two-band model,
since most of these correlated systems have electrons from at least two
different atomic orbitals coexisting at their Fermi surface. The Coulomb
repulsion is taken into account through a local repulsive interaction. Pairing
is considered among quasi- particles in neighbouring sites and we allow for
different symmetries of the order parameter. In order to deal with the strong
local correlations, we use the well known slave boson approach that has proved
very successful for this problem. Here we are interested in obtaining the zero
temperature properties of the model, specifically its phase diagram and the
existence and nature of superconducting quantum critical points. We show that
these can arise by increasing the mixing between the two bands. Since this can
be controlled by external pressure or doping, our results have a direct
relation with experiments. We show that the superconductor-to-normal transition
can be either to a metal, a correlated metal or to an insulator. Also we
compare the relative stability of s and d-wave paired states for different
regions of parameter space and investigate the BCS- BEC crossover in the
two-band lattice model as function of the strength of the pairing interaction.Comment: 21 pages, 14 figure
Superfluid fission dynamics with microscopic approaches
Recent progresses in the description of the latter stage of nuclear fission
are reported. Dynamical effects during the descent of the potential towards
scission and in the formation of the fission fragments are studied with the
time-dependent Hartree-Fock approach with dynamical pairing correlations at the
BCS level. In particular, this approach is used to compute the final kinetic
energy of the fission fragments. Comparison with experimental data on the
fission of 258Fm are made.Comment: Proceeding of the "International Conference on Nuclear Structure and
Related Topics" (NSRT15
Entanglement Entropy and Full Counting Statistics for -Rotating Trapped Fermions
We consider non-interacting fermions in a harmonic potential of
trapping frequency and in a rotating frame at angular frequency
, with . At zero temperature, the fermions
are in the non-degenerate lowest Landau level and their positions are in one to
one correspondence with the eigenvalues of an complex Ginibre
matrix. For large , the fermion density is uniform over the disk of radius
centered at the origin and vanishes outside this disk. We compute
exactly, for any finite , the R\'enyi entanglement entropy of order ,
, as well as the cumulants of order , ,
of the number of fermions in a disk of radius centered at the origin.
For , in the (extended) bulk, i.e., for , we show
that is proportional to the number variance ,
despite the non-Gaussian fluctuations of . This relation breaks down at
the edge of the fermion density, for , where we show
analytically that and have a different
-dependence.Comment: 6 pages + 7 pages (Supplementary material), 2 Figure
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