96,895 research outputs found
Economic Growth And Child Undernutrition
Sebastian Vollmer and colleagues (April, 2014)1 conclude that âthe contribution of economic growth to the reduction in early childhood undernutrition in developing countries is very small, if it exists at allâ. Progress will therefore require a shift from âthe so-called trickle-down approach of a growth-mediated strategyâ to âdirect investments in health and nutritionâ.
Supersolid phases of dipolar bosons in optical lattices with a staggered flux
We present the theoretical mean-field zero-temperature phase diagram of a
Bose-Einstein condensate (BEC) with dipolar interactions loaded into an optical
lattice with a staggered flux. Apart from uniform superfluid, checkerboard
supersolid and striped supersolid phases, we identify several supersolid phases
with staggered vortices, which can be seen as combinations of supersolid phases
found in earlier work on dipolar BECs and a staggered-vortex phase found for
bosons in optical lattices with staggered flux. By allowing for different
phases and densities on each of the four sites of the elementary plaquette,
more complex phase patterns are found.Comment: 11 pages; added references, minor changes in tex
Possible Reentrance of the Fractional Quantum Hall Effect in the Lowest Landau Level
In the framework of a recently developed model of interacting composite
fermions, we calculate the energy of different solid and Laughlin-type liquid
phases of spin-polarized composite fermions. The liquid phases have a lower
energy than the competing solids around the electronic filling factors
nu=4/11,6/17, and 4/19 and may thus be responsible for the fractional quantum
Hall effect at nu=4/11. The alternation between solid and liquid phases when
varying the magnetic field may lead to reentrance phenomena in analogy with the
observed reentrant integral quantum Hall effect.Comment: 4 pages, 3 figures; revised version accepted for publication in Phys.
Rev. Let
Quantum Phases in Partially Filled Landau Levels
We compare the energies of different electron solids, such as bubble crystals
with triangular and square symmetry and stripe phases, to those of correlated
quantum liquids in partially filled intermediate Landau levels. Multiple
transitions between these phases when varying the filling of the top-most
partially filled Landau level explain the observed reentrance of the integer
quantum Hall effect. The phase transitions are identified as first-order. This
leads to a variety of measurable phenomena such as the phase coexistence
between a Wigner crystal and a two-electron bubble phase in a Landau-level
filling-factor range , which has recently been observed in
transport measurements under micro-wave irradiation.Comment: 6 pages, 2 figures; to appear in "Proceedings of the 16th
International Conference on High Magnetic Fields in Semiconductor Physics
(SemiMag-16)
Second Generation of Composite Fermions and the Self-Similarity of the Fractional Quantum Hall Effect
A recently developed model of interacting composite fermions, is used to
investigate different composite-fermion phases. Their interaction potential
allows for the formation of both solid and new quantum-liquid phases, which are
interpreted in terms of second-generation composite fermions and which may be
responsible for the fractional quantum Hall states observed at unusual filling
factors, such as nu=4/11. Projection of the composite-fermion dynamics to a
single level, involved in the derivation of the Hamiltonian of interacting
composite fermions, reveals the underlying self-similarity of the model.Comment: 4 pages, 1 figure; to appear in "Proceedings of the 16th
International Conference on High Magnetic Fields in Semiconductor Physics
(SemiMag-16)", only change with respect to v1: correction in authors line, no
changes in manuscrip
Unitarity of theories containing fractional powers of the d'Alembertian operator
We examine the unitarity of a class of generalized Maxwell U(1) gauge
theories in (2+1) D containing the pseudodifferential operator
, for . We show that only Quantum
Electrodynamics (QED) and its generalization known as Pseudo Quantum
Electrodynamics (PQED), for which and , respectively,
satisfy unitarity. The latter plays an important role in the description of the
electromagnetic interactions of charged particles confined to a plane, such as
in graphene or in hetero-junctions displaying the quantum Hall effect.Comment: 6 pages, no figure
Scaling Approach to the Phase Diagram of Quantum Hall Systems
We present a simple classification of the different liquid and solid phases
of quantum Hall systems in the limit where the Coulomb interaction between the
electrons is significant, i.e. away from integral filling factors. This
classification, and a criterion for the validity of the mean-field
approximation in the charge-density-wave phase, is based on scaling arguments
concerning the effective interaction potential of electrons restricted to an
arbitrary Landau level. Finite-temperature effects are investigated within the
same formalism, and a good agreement with recent experiments is obtained.Comment: 4 pages, 3 figures; to be published in Europhys. Lett.; new version
contains more detailed description of finite-temperature effect
Interaction Induced Quantum Valley Hall Effect in Graphene
We use Pseudo Quantum Electrodynamics (PQED) in order to describe the full
electromagnetic interaction of the p-electrons of graphene in a consistent 2D
formulation. We first consider the effect of this interaction in the vacuum
polarization tensor or, equivalently, in the current correlator. This allows us
to obtain the dc conductivity after a smooth zero-frequency limit is taken in
Kubo's formula.Thereby, we obtain the usual expression for the minimal
conductivity plus corrections due to the interaction that bring it closer to
the experimental value. We then predict the onset of an interaction-driven
spontaneous Quantum Valley Hall effect (QVHE) below a critical temperature of
the order of K. The transverse (Hall) valley conductivity is evaluated
exactly and shown to coincide with the one in the usual Quantum Hall effect.
Finally, by considering the effects of PQED, we show that the electron
self-energy is such that a set of P- and T- symmetric gapped electron energy
eigenstates are dynamically generated, in association with the QVHE.Comment: 5 pages + supplemental materia
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Assessment of mechanical properties and microstructure characterizing techniques in their ability to quantify amount of cold work in 316l alloy
Stress corrosion cracking (SCC) behavior is a matter of concern for structural materials, namely, stainless steels and nickel alloys, in nuclear power plants. High levels of cold work (CW) have shown to both reduce crack initiation times and increase crack growth rates. Cold working has numerous effects on a material, including changes in microstructure, mechanical properties, and residual stress state, yet it is typically reported as a simple percent change in geometry. There is need to develop a strategy for quantitative assessment of cold-work level in order to better understand stress corrosion cracking test data. Five assessment techniques, commonly performed alongside stress corrosion cracking testing (optical microscopy (OM), electron backscatter diffraction (EBSD), X-ray diffraction (XRD), tensile testing, and hardness testing) are evaluated with respect to their ability to quantify the level of CW in a component. The test material is stainless steel 316L that has been cold-rolled to three conditions: 0%, 20%, and 30% CW. Measurement results for each assessment method include correlation with CW condition and repeatability data. Measured values showed significant spatial variation, illustrating that CW level is not uniform throughout a component. Mechanical properties (tensile testing, hardness) were found to correlate most linearly with the amount of imparted CW
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