8,682 research outputs found
Do Bankers Sacrifice Value to Build Empires? Managerial Incentives, Industry Consolidation and Financial Performance
Bank consolidation is a global phenomenon that may enhance stakeholders' value if managers do not sacrifice value to build empires. We find strong evidence of managerial entrenchment at U.S. bank holding companies that have higher levels of managerial ownership, better growth opportunities, poorer financial performance, and smaller asset size. At banks without entrenched management, both asset acquisitions and sales are associated with improved performance. At banks with entrenched management, sales are related to smaller improvements while acquisitions are associated with worse performance. Consistent with scale economies, an increase in assets by internal growth is associated with better performance at most banks. Key Words: consolidation, acquisitions, managerial incentives, efficiency, agency problems, corporate control, stochastic frontier
Non-thermalization in trapped atomic ion spin chains
Linear arrays of trapped and laser cooled atomic ions are a versatile
platform for studying emergent phenomena in strongly-interacting many-body
systems. Effective spins are encoded in long-lived electronic levels of each
ion and made to interact through laser mediated optical dipole forces. The
advantages of experiments with cold trapped ions, including high spatiotemporal
resolution, decoupling from the external environment, and control over the
system Hamiltonian, are used to measure quantum effects not always accessible
in natural condensed matter samples. In this review we highlight recent work
using trapped ions to explore a variety of non-ergodic phenomena in long-range
interacting spin-models which are heralded by memory of out-of-equilibrium
initial conditions. We observe long-lived memory in static magnetizations for
quenched many-body localization and prethermalization, while memory is
preserved in the periodic oscillations of a driven discrete time crystal state.Comment: 14 pages, 5 figures, submitted for edition of Phil. Trans. R. Soc. A
on "Breakdown of ergodicity in quantum systems
A transparent distributed ledger-based certificate revocation scheme for VANETs
The widespread adoption of Cooperative, Connected, and Automated Mobility (CCAM) applications requires the implementation of stringent security mechanisms to minimize the surface of cyber attacks. Authentication is an effective process for validating user identity in vehicular networks. However, authentication alone is not enough to prevent dangerous attack situations. Existing security mechanisms are not able to promptly revoke the credentials of misbehaving vehicles, thus tolerate malicious actors to remain trusted in the system for a long time. The resulting vulnerability window allows the implementation of complex attacks, thus posing a substantial impairment to the security of the vehicular ecosystem. In this paper we propose a Distributed Ledger-based Vehicular Revocation Scheme that improves the state of the art by providing a vulnerability window lower than 1 s, reducing well-behaved vehicles exposure to sophisticated and potentially dangerous attacks. The proposed scheme harnesses the advantages of the underlying Distributed Ledger Technology (DLT) to implement a privacy-aware revocation process while being fully transparent to all participating entities. Furthermore, it meets the critical message processing times defined by EU and US standards, thus closing a critical gap in the current international standards. Theoretical analysis and experimental validation demonstrate the effectiveness and efficiency of the proposed scheme, where DLT streamlines the revocation operation overhead and delivers an economically viable yet scalable solution against cyber attacks on vehicular systems
Beam tests of the gas electron multiplier
We describe the results of systematic measurements, carried out with single and double GEM detectors with printed circuit read-out and having an active area 10x10 cm , both in the laboratory and in a high energy charged particles beam at CERN. Using fast analogue readout electronics, we demonstrate efficiencies for minimum ionizing particles close to 100%, with typical signal/noise ratios above 50 and up to 10 for the single and double GEM configuration, respectively, and a time resolution of 15 ns fwhm. Localization accuracies around 40 mm rms have been obtained for perpendicular tracks, degrading to 200 mm at 20° of incidence to the normal. Operated in a non-flammable gas mixture (argon-carbon dioxide), GEM detectors are robust, light and cheap to manufacture, and offer excellent performances and reliability suited for use in the harsh environments met at high luminosity colliders
Modeling magnetohydrodynamics and non equilibrium SoHO/UVCS line emission of CME shocks
We provide a guideline to interpret the UVCS emission lines (in particular O
VI and Si XII) during shock wave propagation in the outer solar corona. We use
a numerical MHD model performing a set of simulations of shock waves generated
in the corona and from the result we compute the plasma emission for the O VI
and Si XII including the effects of NEI. We analyze the radiative and spectral
properties of our model with the support of a detailed radiation model
including Doppler dimming and an analytical model for shocks, and, finally, we
synthesize the expected O VI 1032A line profile. We explain several spectral
features of the observations like the absence of discontinuities in the O VI
emission during the shock passage, the brightening of Si XII emission and the
width of the lines. We use our model also to give very simple and general
predictions for the strength of the line wings due to the ions shock heating
and on the line shape for Limb CMEs or Halo CMEs. The emission coming from
post-shock region in the solar corona roughly agrees with the emission from a
simple planar and adiabatic shock, but the effect of thermal conduction and the
magnetic field may be important depending on the event parameters. Doppler
dimming significantly influences the O VI emission while Si XII line brightens
mainly because of the shock compression. Significant shock heating is
responsible for the wide and faint component of the O VI line usually observed
which may be taken as a shock signature in the solar corona.Comment: 11 pages, 12 figures, 2 appendixe
Coronal energy release by MHD avalanches. Effects on a structured, active region, multi-threaded coronal loop
A possible key element for large-scale energy release in the solar corona is
an MHD kink instability in a single twisted magnetic flux tube. An initial
helical current sheet fragments in a turbulent way into smaller-scale sheets,
similarly to a nanoflare storm. As the loop expands in the radial direction
during the relaxation process, an unstable loop can disrupt nearby stable loops
and trigger an MHD avalanche. Exploratory investigations have been conducted in
previous works with relatively simplified loop configurations. Here, we address
a more realistic environment that comprehensively accounts for most of the
physical effects involved in a stratified atmosphere, typical of an active
region. The question is whether the avalanche process will be triggered, with
what timescales, and how it will develop, as compared with the original,
simpler approach. Three-dimensional MHD simulations describe the interaction of
magnetic flux tubes, which have a stratified atmosphere, including
chromospheric layers, the thin transition region to the corona, and the related
transition from high-beta to low-beta regions. The model also includes the
effects of thermal conduction and of optically thin radiation. Our simulations
address the case where one flux tube among a few is twisted at the footpoints
faster than its neighbours. We show that this flux tube becomes kink unstable
first, in conditions in agreement with those predicted by analytical models. It
rapidly involves nearby stable tubes, instigating significant magnetic
reconnection and dissipation of energy as heat. The heating determines the
development of chromospheric evaporation, while the temperature rises up to
about 10 MK, close to microflares observations. This work confirms that
avalanches are a viable mechanism for the storing and release of magnetic
energy in plasma confined in closed coronal loops, as a result of photospheric
motions.Comment: 16 pages, 16 figure
Chromospheric evaporation and phase mixing of Alfvén waves in coronal loops
This work has received support from the UK Science and Technology Facilities Council (Consolidated Grant ST/K000950/1), the European Union Horizon 2020 research and innovation programme (grant agreement No. 647214) and the Research Council of Norway through its Centres of Excellence scheme, project number 262622.Context. Phase mixing of AlfvĂ©n waves has been studied extensively as a possible coronal heating mechanism but without the full thermodynamic consequences considered self-consistently. It has been argued that in some cases, the thermodynamic feedback of the heating could substantially affect the transverse density gradient and even inhibit the phase mixing process. Aims. In this paper, for the first time, we use magnetohydrodynamic (MHD) simulations with the appropriate thermodynamical terms included to quantify the evaporation following heating by phase mixing of AlfvĂ©n waves in a coronal loop and the effect of this evaporation on the transverse density profile. Methods. The numerical simulations were performed using the Lagrangian Remap code Lare2D. We set up a 2D loop model consisting of a field-aligned thermodynamic equilibrium and a cross-field (background) heating profile. A continuous, sinusoidal, high-frequency AlfvĂ©n wave driver was implemented. As the AlfvĂ©n waves propagate along the field, they undergo phase mixing due to the cross-field density gradient in the coronal part of the loop. We investigated the presence of field-aligned flows, heating from the dissipation of the phase-mixed AlfvĂ©n waves, and the subsequent evaporation from the lower atmosphere. Results. We find that phase mixing of AlfvĂ©n waves leads to modest heating in the shell regions of the loop and evaporation of chromospheric material into the corona with upflows of the order of only 5â20 m sâ1. Although the evaporation leads to a mass increase in the shell regions of the loop, the effect on the density gradient and, hence, on the phase mixing process, is insignificant. Conclusions. This paper self-consistently investigates the effect of chromospheric evaporation on the cross-field density gradient and the phase mixing process in a coronal loop. We found that the effects in our particular setup (small amplitude, high frequency waves) are too small to significantly change the density gradient.PostprintPeer reviewe
Thermodynamical features of multifragmentation in peripheral Au + Au Collisions at 35 A.MeV
The distribution of fragments produced in events involving the
multifragmentation of excited sources is studied for peripheral Au + Au
reactions at 35 A.MeV.
The Quasi-Projectile has been reconstructed from its de-excitation products.
An isotropic emission in its rest frame has been observed, indicating that an
equilibrated system has been formed. The excitation energy of the
Quasi-Projectile has been determined via calorimetry.
A new event by event effective thermometer is proposed based on the energy
balance. A peak in the energy fluctuations is observed related to the heat
capacity, suggesting that the system undergoes a liquid-gas type phase
transition at an excitation energy about 5 A.MeV and a temperature 4 - 6 MeV,
dependent on the freeze-out hypothesis. By analyzing different regions of the
Campi-plot, the events associated with the liquid and gas phases as well as the
critical region are thermodynamically characterized.
The critical exponents, tau, beta,gamma, extracted from the high moments of
the charge distribution are consistent with a liquid-gas type phase transition.Comment: 44 pages, 16 Postscript figures, Fig14_nucl-ex.eps in colors, to be
published in Nucl.Phys.A (1999
Kepler423b: a half-Jupiter mass planet transiting a very old solar-like star
We report the spectroscopic confirmation of the Kepler object of interest
KOI-183.01 (Kepler-423b), a half-Jupiter mass planet transiting an old
solar-like star every 2.7 days. Our analysis is the first to combine the full
Kepler photometry (quarters 1-17) with high-precision radial velocity
measurements taken with the FIES spectrograph at the Nordic Optical Telescope.
We simultaneously modelled the photometric and spectroscopic data-sets using
Bayesian approach coupled with Markov chain Monte Carlo sampling. We found that
the Kepler pre-search data conditioned (PDC) light curve of KOI-183 exhibits
quarter-to-quarter systematic variations of the transit depth, with a
peak-to-peak amplitude of about 4.3 % and seasonal trends reoccurring every
four quarters. We attributed these systematics to an incorrect assessment of
the quarterly variation of the crowding metric. The host star KOI-183 is a G4
dwarf with M_\rm{Sun},
R_\rm{Sun}, K, dex, and with
an age of Gyr. The planet KOI-183b has a mass of
M and a radius of
R, yielding a planetary bulk
density of g/cm. The radius of KOI-183b
is consistent with both theoretical models for irradiated coreless giant
planets and expectations based on empirical laws. The inclination of the
stellar spin axis suggests that the system is aligned along the line of sight.
We detected a tentative secondary eclipse of the planet at a 2-
confidence level ( ppm) and found that the
orbit might have a small non-zero eccentricity of .
With a Bond albedo of , KOI-183b is one of the
gas-giant planets with the lowest albedo known so far.Comment: 13 pages, 13 figures, 5 tables. Accepted for publication in A&A.
Planet designation changed from KOI-183b to Kepler-423
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