2,812 research outputs found
An application of -adic integration to the dynamics of a birational transformation preserving a fibration
Let be a birational transformation of a
projective manifold whose Kodaira dimension is non-negative. We
show that, if there exist a meromorphic fibration and a pseudo-automorphism which preserves a
big line bundle and such that , then
has finite order.
As a corollary we show that, for projective irreducible symplectic manifolds
of type or generalized Kummer, the first dynamical degree
characterizes the birational transformations admitting a Zariski-dense orbit
On the primitivity of birational transformations of irreducible symplectic manifolds
Let be a bimeromorphic transformation of a
complex irreducible symplectic manifold . Some important dynamical
properties of are encoded by the induced linear automorphism of
. Our main result is that a bimeromorphic transformation such
that has at least one eigenvalue with modulus doesn't admit any
invariant fibration (in particular its generic orbit is Zariski-dense)
Low-dimensional modelling of flame dynamics in heated microchannels
This paper presents simulations of stoichiometric methane/air premixed flames
into a microchannel at atmospheric pressure. These simulations result from
numerical resolutions of reduced-order models. Indeed, combustion control into
microchannels would be allowed by fast simulations that in turn enable
real-time adjustments of the device's parameters. Former experimental studies
reported the occurrence of a Flame Repetitive Extinction/Ignition (FREI)
phenomenon provided that a temperature gradient is sustained at the channel's
walls. Conducting unsteady one-dimensional simulations including complex
chemistry, a late numerical study tried to explain the occurrence of this
phenomenon. The present study therefore explores low-dimensional models that
potentially reproduce the FREI phenomenon. Provided a calibration of some
empirical constants, an unsteady two-dimensional model including one-step
chemical reaction is shown to decently reproduce the FREI regime all along the
range of mixture flow rates investigated by the experimental studies.
Complementing the aforementioned numerical study, furthermore, when the
channel's diameter is varied, the two-dimensional model unveils an unstable
regime that a one-dimensional model cannot capture. As two-dimensional
hydrodynamics appears to play a key role into the flame's dynamics, therefore
the heat rate released by the microcombustor, one-dimensional models are not
believed to deliver an adequate strategy of combustion control into such
microchannels.Comment: 37 pages, 12 figure
Reaction spreading on percolating clusters
Reaction-diffusion processes in two-dimensional percolating structures are
investigated. Two different problems are addressed: reaction spreading on a
percolating cluster and front propagation through a percolating channel. For
reaction spreading, numerical data and analytical estimates show a power-law
behavior of the reaction product as M(t) \sim t^dl, where dl is the
connectivity dimension. In a percolating channel, a statistically stationary
traveling wave develops. The speed and the width of the traveling wave are
numerically computed. While the front speed is a low-fluctuating quantity and
its behavior can be understood using a simple theoretical argument, the front
width is a high-fluctuating quantity showing a power-law behavior as a function
of the size of the channelComment: 7 pages, 8 figure
Metabolic Algorithm with Time-varying Reaction Maps
A symbolic-based approach to modelling biochemical processes and cellular
dynamics is likely to turn useful in computational biology, where attempts to represent
the cell as a huge, complex dynamic system must trade with the linguistic nature of the
DNA and the individual behavior of the organelles living within. The early version of
the metabolic algorithm gave a first answer to the problem of representing oscillatory
biological phenomena, so far being treated with traditional (differential) mathematical
tools, in terms of rewriting systems. We are now working on a further version of this
algorithm, in which the rule application is tuned by reaction maps depending on the
specific phenomenon under consideration. Successful simulations of the Brusselator, the
Lotka-Volterra population dynamics and the PKC activation foster potential applications
of the algorithm in systems biology
Modelling of combustion and knock onset risk in a high-performance turbulent jet ignition engine
The reduction of CO2 emissions, and hence of fuel consumption, is currently a key driver for the development
of innovative SI engines for passenger car applications. In recent years, motorsport technical regulations in the
highest categories have seen the introduction of limits concerning the fuel flow rate and the total amount of fuel
per race, thus driving engine development toward further reduction of specific fuel consumption. Among the
different techniques that can be shared between conventional and high-performance SI engines, turbocharging,
compression ratio increase and Turbulent Jet Ignition (TJI) have shown a significant potential for fuel consumption reduction. The combination of turbocharging and compression ratio increase, however, can promote the
onset of knocking combustion, with detrimental effects on engine’s efficiency and durability. Additionally, engines equipped with TJI systems show unusual combustion development and knock onset.
In this study a methodology for the 3D-CFD modelling of combustion and knock onset risk was developed for a
high-performance turbocharged engine featuring a passive TJI system. First, a comprehensive numerical study
was carried out in a commercially available software, CONVERGE 2.4, in order to develop a 3D-CFD model
able to reproduce the available experimental data. The resulting 3D-CFD model was then validated on different
working conditions featuring different spark advances. Lastly, a methodology for the assessment of knock onset
risk was developed, which led to the definition of two novel knock-risk indexes based on the progress of chemical
reactions within the combustion chamber. The proposed knock-risk indexes showed good agreement with the
experimental data
GRB 980425, SN1998bw and the EMBH model
The EMBH model, previously developed using GRB 991216 as a prototype, is here
applied to GRB 980425. We fit the luminosity observed in the 40-700 keV, 2-26
keV and 2-10 keV bands by the BeppoSAX satellite. In addition we present a
novel scenario in which the supernova SN1998bw is the outcome of an ``induced
gravitational collapse'' triggered by GRB 980425, in agreement with the
GRB-Supernova Time Sequence (GSTS) paradigm (Ruffini et al. 2001c). A further
outcome of this astrophysically exceptional sequence of events is the formation
of a young neutron star generated by the SN1998bw event. A coordinated
observational activity is recommended to further enlighten the underlying
scenario of this most unique astrophysical system.Comment: 10 pages, 3 figures, in the Proceedings of the 34th COSPAR scientific
assembly, Elsevier. Fixed some typos in this new versio
- …