1,321 research outputs found
Exploring the Nexus between Banking Sector Reform and Performance: Evidence from Newly Acceded EU Countries
The aim of this study is to examine the relationship between banking sector reform and bank performance – measured in terms of efficiency, total factor productivity growth and net interest margin – accounting for the effects through competition and bank risk-taking. To this end, we develop an empirical model of bank performance and draw on recent econometric advances to consistently estimate it. The model is applied to bank panel data from ten newly acceded EU countries. The results indicate that both banking sector reform and competition exert a positive impact on bank efficiency, while the effect of reform on total factor productivity growth is significant only toward the end of the reform process. Finally, the effect of capital and credit risk on bank performance is in most cases negative, while it seems that higher liquid assets reduce the efficiency and productivity of banks.Bank performance; Banking sector reform; Competition; Risk-taking
Constraining supermassive primordial black holes with magnetically induced gravitational waves
Primordial black holes (PBHs) can answer a plethora of cosmic conundra, among
which the origin of the cosmic magnetic fields. In particular, supermassive
PBHs with masses and furnished with a
plasma-disk moving around them can generate through the Biermann battery
mechanism a seed primordial magnetic field which can later be amplified so as
to provide the magnetic field threading the intergalactic medium. In this
Letter, we derive the gravitational wave (GW) signal induced by the magnetic
anisotropic stress of such a population of magnetised PBHs. Interestingly
enough, by using GW constraints from Big Bang Nucleosynthesis (BBN) and an
effective model for the galactic/turbulent dynamo amplification of the magnetic
field, we set a conservative upper bound constraint on the abundances of
supermassive PBHs at formation time, as a function of
the their masses, namely that . Remarkably, these
constraints are comparable, and, in some mass ranges, even tighter compared to
the constraints on from large-scale structure (LSS)
probes; hence promoting the portal of magnetically induced GWs as a new probe
to explore the enigmatic nature of supermassive PBHs.Comment: 5 pages, 2 figures (comments are welcome
Magnetoresistance of atomic-sized contacts: an ab-initio study
The magnetoresistance (MR) effect in metallic atomic-sized contacts is
studied theoretically by means of first-principle electronic structure
calculations. We consider three-atom chains formed from Co, Cu, Si, and Al
atoms suspended between semi-infinite Co leads. We employ the screened
Korringa-Kohn-Rostoker Green's function method for the electronic structure
calculation and evaluate the conductance in the ballistic limit using the
Landauer approach. The conductance through the constrictions reflects the
spin-splitting of the Co bands and causes high MR ratios, up to 50%. The
influence of the structural changes on the conductance is studied by
considering different geometrical arrangements of atoms forming the chains. Our
results show that the conductance through s-like states is robust against
geometrical changes, whereas the transmission is strongly influenced by the
atomic arrangement if p or d states contribute to the current.Comment: Revised version, presentation of results is improved, figure 2 is
splitted to two figure
Acousto-optic interaction enhancement in dual photonic-phononic cavities
Light control through elastic waves is a well established and mature technology. The underlying mechanism is the scattering of light due to the dynamic modulation of the refractive index and the material interfaces caused by an elastic wave, the so-called acousto-optic interaction. This interaction can be enhanced in appropriately designed structures that simultaneously localize light and elastic waves in the same region of space and operate as dual optical-elastic cavities, often called phoxonic or optomechanical cavities. Typical examples of phoxonic cavities are multilayer films with a dielectric sandwiched between two Bragg mirrors or, in general, defects in macroscopically periodic structures that exhibit dual band gaps for light and elastic waves. In the present work we consider dielectric particles as phoxonic cavities and study the influence of elastic eigenmode vibrations on the optical Mie resonances. An important issue is the excitation of elastic waves in such submicron particles and, in this respect, we analyze the excitation of high-frequency vibrations following thermal expansion induced by the absorption of a femtosecond laser pulse. For spherical particles, homogeneous thermalization leads to excitation of the particle breathing modes. We report a thorough study of the acousto-optic interaction, correct to all orders in the acousto-optic coupling parameter, by means of rigorous full electrodynamic and elastodynamic calculations, in both time and frequency domains. Our results show that, under double elastic-optical resonance conditions, strong acousto-optic interaction takes place and results in large dynamical shifts of the high-Q optical Mie resonances, manifested through multiphonon exchange mechanisms
Ballistic Spin Injection from Fe into ZnSe and GaAs with a (001), (111), and (110) orientation
We present first-principles calculations of ballistic spin injection in
Fe/GaAs and Fe/ZnSe junctions with orientation (001), (111), and (110). We find
that the symmetry mismatch of the Fe minority-spin states with the
semiconductor conduction states can lead to extremely high spin polarization of
the current through the (001) interface for hot and thermal injection
processes. Such a symmetry mismatch does not exist for the (111) and (110)
interfaces, where smaller spin injection efficiencies are found. The presence
of interface states is found to lower the current spin polarization, both with
and without a Schottky barrier. Finally, a higher bias can also affect the spin
injection efficiency.Comment: 12 pages, 18 figure
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