1,490 research outputs found
The performance effects of board heterogeneity: What works for EU banks?
We examine the impact of board heterogeneity on the performance of EU listed banks in the wake of the global financial crisis. In a comprehensive set-up, we consider standard board features (type, tenure, size, and age of board members) as well as board diversity features (gender diversity, employee representation, internationalisation, and age diversity). We propose a diversity index, which summarises the different dimensions of diversity and control for unobserved heterogeneity and reverse causality. Our analysis uncovers a complex relationship between board heterogeneity and bank performance, which is influenced by market conditions and by national culture. Overall board diversity does not seem to affect bank performance, but it does decrease performance variability during the Eurozone crisis and in countries culturally more open to diversity. Different board and diversity features have a positive impact on bank performance (size, tenure, and employee representation); the relationship is non-linear, with the effect of diversity being more relevant when there is a significant proportion of minority representatives. While substantial board internationalisation has a negative impact on bank performance, the presence of foreign directors appears to be less detrimental during the Eurozone crisis and in countries that are more welcoming towards diversity
An Alkali-Vapor Cell with Metal Coated Windows for Efficient Application of an Electric Field
We describe the implementation of a cylindrical T-shaped alkali-vapor cell
for laser spectroscopy in the presence of a longitudinal electric field. The
two windows are used as two electrodes of the high-voltage assembly, which is
made possible by a metallic coating which entirely covers the inner and outer
sides of the windows except for a central area to let the laser beams in and
out of the cell. This allows very efficient application of the electric field,
up to 2 kV/cm in a rather dense superheated vapor, even when significant
photoemission takes place at the windows during pulsed laser irradiation. The
body of the cell is made of sapphire or alumina ceramic to prevent large
currents resulting from surface conduction observed in cesiated glass cells.
The technique used to attach the monocrystalline sapphire windows to the cell
body causes minimal stress birefringence in the windows. In addition,
reflection losses at the windows can be made very small. The vapor cell
operates with no buffer gas and has no magnetic part. The use of this kind of
cell has resulted in an improvement of the signal-to-noise ratio in the
measurement of Parity Violation in cesium vapor underway at ENS, Paris. The
technique can be applied to other situations where a brazed assembly would give
rise to unacceptably large birefringence in the windows
Complete hyperfine Paschen-Back regime at relatively small magnetic fields realized in Potassium nano-cell
A one-dimensional nano-metric-thin cell (NC) filled with potassium metal has
been built and used to study optical atomic transitions in external magnetic
fields. These studies benefit from the remarkable features of the NC allowing
one to use - and -methods for effective investigations of
individual transitions of the K D_1 line. The methods are based on strong
narrowing of the absorption spectrum of the atomic column of thickness L equal
to and to (with \lambda = 770\un{nm} being the resonant
laser radiation wavelength). In particular, for a -polarized radiation
excitation the -method allows us to resolve eight atomic transitions
(in two groups of four atomic transitions) and to reveal two remarkable
transitions that we call Guiding Transitions (GT). The probabilities of all
other transitions inside the group (as well as the frequency slope versus
magnetic field) tend to the probability and to the slope of GT. Note that for
circular polarization there is one group of four transitions and GT do not
exist. Among eight transitions there are also two transitions (forbidden for
= 0) with the probabilities undergoing strong modification under the
influence of magnetic fields. Practically the complete hyperfine Paschen-Back
regime is observed at relatively low (\sim 1\un{kG}) magnetic fields. Note
that for K line GT are absent. Theoretical models describe the experiment
very well.Comment: 6 page
Nonlinear magneto-optical resonances at D1 excitation of 85Rb and 87Rb in an extremely thin cell
Nonlinear magneto-optical resonances have been measured in an extremely thin
cell (ETC) for the D1 transition of rubidium in an atomic vapor of natural
isotopic composition. All hyperfine transitions of both isotopes have been
studied for a wide range of laser power densities, laser detunings, and ETC
wall separations. Dark resonances in the laser induced fluorescence (LIF) were
observed as expected when the ground state total angular momentum F_g was
greater than or equal to the excited state total angular momentum F_e. Unlike
the case of ordinary cells, the width and contrast of dark resonances formed in
the ETC dramatically depended on the detuning of the laser from the exact
atomic transition. A theoretical model based on the optical Bloch equations was
applied to calculate the shapes of the resonance curves. The model averaged
over the contributions from different atomic velocity groups, considered all
neighboring hyperfine transitions, took into account the splitting and mixing
of magnetic sublevels in an external magnetic field, and included a detailed
treatment of the coherence properties of the laser radiation. Such a
theoretical approach had successfully described nonlinear magneto-optical
resonances in ordinary vapor cells. Although the values of certain model
parameters in the ETC differed significantly from the case of ordinary cells,
the same physical processes were used to model both cases. However, to describe
the resonances in the ETC, key parameters such as the transit relaxation rate
and Doppler width had to be modified in accordance with the ETC's unique
features. Agreement between the measured and calculated resonance curves was
satisfactory for the ETC, though not as good as in the case of ordinary cells.Comment: v2: substantial changes and expanded theoretical model; 13 pages, 10
figures; accepted for publication in Physical Review
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