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 $\Delta E(\mathbf{k})\sim 100\div150\,{\rm meV}$ depending on the electron concentration $n_{e}$ 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