15,109 research outputs found
Modelling unemployment in the presence of excess labour supply:An application to Egypt
Due to its pyramid population structure, Egypt needs to create jobs at
a high pace to absorb the many new entrants at its labour market.
This article structurally models and quantifies the impact of these
demographic shocks and the shedding of public sector jobs on
unemployment. The findings indicate that Egypt needs to grow at 5%
for many years to come. Job creation better occurs in the private than
in the public sector. Egypt’s public sector has been driving up
government expenditures disproportionably, not only because of the
numerous public sector employees but also because of high public wage
growth.
Keywords: Demography, labour supply, employment, public sector
employment, public finance.
Editorial: Transport and Tourism: a Weak Symbiosis. An Introduction to the Special Issue
“Tourism’s very existence depends on transport. Still, researchers in transportation and logistic
Energy-Momentum dispersion relation of plasmarons in bilayer graphene
The relation between the energy and momentum of plasmarons in bilayer
graphene is investigated within the Overhauser approach, where the
electron-plasmon interaction is described as a field theoretical problem. We
find that the Dirac-like spectrum is shifted by depending on the electron concentration and
electron momentum. The shift increases with electron concentration as the
energy of plasmons becomes larger. The dispersion of plasmarons is more
pronounced than in the case of single layer graphene, which is explained by the
fact that the energy dispersion of electrons is quadratic and not linear. We
expect that these predictions can be verified using angle-resolved
photoemission spectroscopy (ARPES).Comment: 4 pages, 3 figure
The interaction between a superconducting vortex and an out-of-plane magnetized ferromagnetic disk: influence of the magnet geometry
The interaction between a superconducting vortex in a type II superconducting
film (SC) and a ferromagnet (FM) with out-of-plane magnetization is
investigated theoretically within the London approximation. The dependence of
the interaction energy on the FM-vortex distance, film thickness and different
geometries of the magnetic structures: disk, annulus(ring), square and triangle
are calculated. Analytic expressions and vectorplots of the current induced in
the SC due to the presence of the FM are presented. For a FM disk with a
cavity, we show that different local minima for the vortex position are
possible, enabling the system to be suitable to act as a qubit. For FMs with
sharp edges, like e.g. for squares and triangles, the vortex prefers to enter
its equilibrium position along the corners of the magnet.Comment: Preprint, 10 pages, 10 figures, submitted to Phys. Rev.
Quantum states in a magnetic anti-dot
We study a new system in which electrons in two dimensions are confined by a
non homogeneous magnetic field. The system consists of a heterostructure with
on top of it a superconducting disk. We show that in this system electrons can
be confined into a dot region. This magnetic anti-dot has the interesting
property that the filling of the dot is a discrete function of the magnetic
field. The circulating electron current inside and outside the anti-dot can be
in opposite direction for certain bound states. And those states exhibit a
diamagnetic to paramagnetic transition with increasing magnetic field. The
absorption spectrum consists of many peaks, some of which violate Kohn's
theorem, and which is due to the coupling of the center of mass motion with the
other degrees of freedom.Comment: 6 pages, 12 ps figure
Field-enhanced critical parameters in magnetically nanostructured superconductors
Within the phenomenological Ginzburg-Landau theory, we demonstrate the
enhancement of superconductivity in a superconducting film, when nanostructured
by a lattice of magnetic particles. Arrays of out-of-plane magnetized dots
(MDs) extend the critical magnetic field and critical current the sample can
sustain, due to the interaction of the vortex-antivortex pairs and surrounding
supercurrents induced by the dots and the external flux lines. Depending on the
stability of the vortex-antivortex lattice, a peak in the Hext-T boundary is
found for applied integer and rational matching fields, which agrees with
recent experiments [Lange et al., Phys. Rev. Lett. 90, 197006 (2003)]. Due to
compensation of MDs- and Hext-induced currents, we predict the field-shifted
jc-Hext characteristics, as was actually realized in previous experiment but
not commented on [Morgan and Ketterson, Phys. Rev. Lett. 80, 3614 (1998)].Comment: 8 pages, 5 figures, to appear in Europhysics Letter
Effect of grain boundary on the buckling of graphene nanoribbons
The buckling of graphene nano-ribbons containing a grain boundary is studied
using atomistic simulations where free and supported boundary conditions are
invoked. We found that when graphene contains a small angle grain boundary the
buckling strains are larger when the ribbons with free (supported) boundary
condition are subjected to compressive tension parallel (perpendicular) to the
grain boundary. The shape of the deformations of the buckled graphene
nanoribbons depends on the boundary conditions and the presence of the grain
boundary and the direction of applied in-plane compressive tension. Large angle
grain boundary results in smaller buckling strains as compared to perfect
graphene or to a small angle grain boundary.Comment: 4 pages, 3 figures, To appear in Applied Physics Letter
Graphene on hexagonal lattice substrate: Stress and Pseudo-magnetic field
Moir'e patterns in the pseudo-magnetic field and in the strain profile of
graphene (GE) when put on top of a hexagonal lattice substrate are predicted
from elasticity theory. %which are confirmed by atomistic simulations. The van
der Waals (vdW) interaction between GE and the substrate induces out-of-plane
deformations in graphene which results in a strain field, and consequently in a
pseudo-magnetic field. When the misorientation angle is about 0.5 deg. a
three-fold symmetric strain field is realized that results in a pseudo-magnetic
field very similar to the one proposed by F. Guinea, M. I. Katsnelson, and A.
K. Geim [Nat. Phys. 6, 30 (2010)]. Our results show that the periodicity and
length of the pseudo-magnetic field can be tuned in GE by changing the
misorientation angle and substrate adhesion parameters and a considerable
energy gap (23 meV) can be obtained due to out-of-plane deformation of graphene
which is in the range of recent experimental measurements (20-30 meV).Comment: 5 pages, 3 figure
- …