5,477 research outputs found
Preasymptotic multiscaling in the phase-ordering dynamics of the kinetic Ising model
The evolution of the structure factor is studied during the phase-ordering
dynamics of the kinetic Ising model with conserved order parameter. A
preasymptotic multiscaling regime is found as in the solution of the
Cahn-Hilliard-Cook equation, revealing that the late stage of phase-ordering is
always approached through a crossover from multiscaling to standard scaling,
independently from the nature of the microscopic dynamics.Comment: 11 pages, 3 figures, to be published in Europhys. Let
Breaking degeneracy in jet dynamics: multi-epoch joint modelling of the BL Lac PKS 2155-304
Supermassive black holes can launch powerful jets which can be some of the
most luminous multi-wavelength sources; decades after their discovery their
physics and energetics are still poorly understood. The past decade has seen a
dramatic improvement in the quality of available data, but despite this
improvement the semi-analytical modelling of jets has advanced slowly: simple
one-zone models are still the most commonly employed method of interpreting
data, in particular for AGN jets. These models can roughly constrain the
properties of jets but they cannot unambiguously couple their emission to the
launching regions and internal dynamics, which can be probed with simulations.
However, simulations are not easily comparable to observations because they
cannot yet self-consistently predict spectra. We present an advanced
semi-analytical model which accounts for the dynamics of the whole jet,
starting from a simplified parametrization of Relativistic Magnetohydrodynamics
in which the magnetic flux is converted into bulk kinetic energy. To benchmark
the model we fit six quasisimultaneous, multi-wavelength spectral energy
distributions of the BL Lac PKS 2155-304 obtained by the TANAMI program, and we
address the degeneracies inherent to such a complex model by employing a
state-of-the-art exploration of parameter space, which so far has been mostly
neglected in the study of AGN jets. We find that this new approach is much more
effective than a single-epoch fit in providing meaningful constraints on model
parameters.Comment: Accepted for publication on MNRA
Broadband Multi-wavelength Properties of M87 during the 2017 Event Horizon Telescope Campaign
Attosecond screening dynamics mediated by electron-localization
Transition metals with their densely confined and strongly coupled valence
electrons are key constituents of many materials with unconventional
properties, such as high-Tc superconductors, Mott insulators and
transition-metal dichalcogenides. Strong electron interaction offers a fast and
efficient lever to manipulate their properties with light, creating promising
potential for next-generation electronics. However, the underlying dynamics is
a fast and intricate interplay of polarization and screening effects, which is
poorly understood. It is hidden below the femtosecond timescale of electronic
thermalization, which follows the light-induced excitation. Here, we
investigate the many-body electron dynamics in transition metals before
thermalization sets in. We combine the sensitivity of intra-shell transitions
to screening effects with attosecond time resolution to uncover the interplay
of photo-absorption and screening. First-principles time-dependent calculations
allow us to assign our experimental observations to ultrafast electronic
localization on d-orbitals. The latter modifies the whole electronic structure
as well as the collective dynamic response of the system on a timescale much
faster than the light-field cycle. Our results demonstrate a possibility for
steering the electronic properties of solids prior to electron thermalization,
suggesting that the ultimate speed of electronic phase transitions is limited
only by the duration of the controlling laser pulse. Furthermore, external
control of the local electronic density serves as a fine tool for testing
state-of-the art models of electron-electron interactions. We anticipate our
study to facilitate further investigations of electronic phase transitions,
laser-metal interactions and photo-absorption in correlated electron systems on
its natural timescale
Serotonin signaling contribution to an evolutionary success: the jaw joint of vertebrates
Serotonin (5-HT) is an ancient molecule that appeared very early during evolution, and it is present in different phyla. The
5-HT signaling system includes several G-coupled receptors and it is widely conserved in vertebrates. 5-HT is implicated in
an astonishing number of biological processes and it has a key role as a morphogen in several complex networks during
development before it can act as a neurotransmitter. Recent advances on how serotonin signaling can influence early
development and its role in vertebrate morphogenesis come from mice and Xenopus. The emergence of jawed vertebrates
(gnathostomes) from jawless vertebrates (agnathans) represents a major event in the evolution of vertebrates. The acquisition
of a jaw is assumed to have occurred after the split between gnathostomes and jawless vertebrates. A crucial question
concerns what changes were introduced in the developmental patterning programme to obtain a jaw joint that is one of the
most innovative inventions in the history of vertebrates. Molecular and developmental studies performed in Xenopus revealed
for the first time that serotonin, through the 5-HT2B receptor signaling, is both sufficient and necessary to modulate the
shape and functionality of the jaw, including the jaw joint. Accordingly, serotonin can be added to the complex interactive
network of extrinsic factors that regulates mandibular arch development, thus contributing to one of the major vertebrate
successes in evolution
Retrofitting unreinforced masonry by steel fiber reinforced mortar coating: uniaxial and diagonal compression tests
AbstractThin layers of mortar reinforced with steel fibers can be applied on one or both sides of bearing walls as an effective seismic strengthening of existing masonry buildings. To assess the effectiveness of this technique, an experimental study on masonry sub-assemblages was carried out at the University of Brescia. This paper summarizes and discusses the main results of the investigation, which included mechanical characterization tests on masonry and its components as well as on the Steel Fiber Reinforced Mortar (SFRM) used to retrofit the masonry samples. Uniaxial and diagonal compression tests were carried out on both unstrengthened wallets and masonry samples retrofitted with 25 mm thick SFRM coating. Both single-sided and double-sided retrofitting configurations for application on wall surfaces were considered. The results highlighted the ability of the technique to improve the compressive and the shear behavior of masonry, even in case of single-sided strengthening. Moreover, no premature debonding of coating was observed. Lastly, the manuscript presents the results of a numerical investigation that was performed both to simulate the diagonal compression tests described in the first part of the paper and to predict the response of panels with different strengthening configurations
Effects of fuel cetane number on the structure of diesel spray combustion: An accelerated Eulerian stochastic fields method
An Eulerian stochastic fields (ESF) method accelerated with the chemistry coordinate mapping (CCM) approach for modelling spray combustion is formulated, and applied to model diesel combustion in a constant volume vessel. In ESF-CCM, the thermodynamic states of the discretised stochastic fields are mapped into a low-dimensional phase space. Integration of the chemical stiff ODEs is performed in the phase space and the results are mapped back to the physical domain. After validating the ESF-CCM, the method is used to investigate the effects of fuel cetane number on the structure of diesel spray combustion. It is shown that, depending of the fuel cetane number, liftoff length is varied, which can lead to a change in combustion mode from classical diesel spray combustion to fuel-lean premixed burned combustion. Spray combustion with a shorter liftoff length exhibits the characteristics of the classical conceptual diesel combustion model proposed by Dec in 1997 (http://dx.doi.org/10.4271/970873), whereas in a case with a lower cetane number the liftoff length is much larger and the spray combustion probably occurs in a fuel-lean-premixed mode of combustion. Nevertheless, the transport budget at the liftoff location shows that stabilisation at all cetane numbers is governed primarily by the auto-ignition process
Evidence for an expanding corona based on spectral-timing modelling of multiple black hole X-ray binaries
PS-318 Are Antenatal Corticosteroids Less Effective In Twins Than In Singletons? A Cohort Study In The Italian Neonatal Network
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