5,697 research outputs found
Frictional Collisions Off Sharp Objects
This work develops robust contact algorithms capable of dealing with multibody nonsmooth contact
geometries for which neither normals nor gap functions can be defined. Such situations arise
in the early stage of fragmentation when a number of angular fragments undergo complex collision
sequences before eventually scattering. Such situations precludes the application of most contact
algorithms proposed to date
Controllability of a viscoelastic plate using one boundary control in displacement or bending
In this paper we consider a viscoelastic plate (linear viscoelasticity of the
Maxwell-Boltzmann type) and we compare its controllability properties with the
(known) controllability of a purely elastic plate (the control acts on the
boundary displacement or bending). By combining operator and moment methods, we
prove that the viscoelastic plate inherits the controllability properties of
the purely elastic plate
Modelling and solutions to the linear stability of a detonation wave in the kinetic frame
Artigo publicado num número especial da revista.The analysis of linear stability of a steady detonation wave
is formulated for the first time at the kinetic level in the frame
of the Boltzmann equation extended to reacting gases. Within
this context and for a reversible reaction, the stability problem is carried out,
in agreement with most classical papers on gas detonation, through a normal mode approach
for the one-dimensional disturbances of the steady wave solution, and an
acoustic radiation condition at the final equilibrium as closure condition.
The proposed modelling leads to an initial value problem,
constituted by the linearized reactive Euler equations in the perturbed shock frame
with related Rankine-Hugoniot conditions, which can be solved by
means of a proper numerical technique.
An application is provided for an elementary bimolecular reaction.Centro de Matemática da Universidade do MinhoFundação para a Ciência e a Tecnologia (FCT)Italian INDAM-GNF
Evolution of the fine-structure constant in runaway dilaton models
We study the detailed evolution of the fine-structure constant in
the string-inspired runaway dilaton class of models of Damour, Piazza and
Veneziano. We provide constraints on this scenario using the most recent
measurements and discuss ways to distinguish it from alternative
models for varying . For model parameters which saturate bounds from
current observations, the redshift drift signal can differ considerably from
that of the canonical CDM paradigm at high redshifts. Measurements of
this signal by the forthcoming European Extremely Large Telescope (E-ELT),
together with more sensitive measurements, will thus dramatically
constrain these scenarios.Comment: 11 pages, 4 figure
The worldwide costs of marine protected areas
Declines in marine harvests, wildlife, and habitats have prompted calls at both the 2002 World Summit on Sustainable Development and the 2003 World Parks Congress for the establishment of a global system of marine protected areas (MPAs). MPAs that restrict fishing and other human activities conserve habitats and populations and, by exporting biomass, may sustain or increase yields of nearby fisheries. Here we provide an estimate of the costs of a global MPA network, based on a survey of the running costs of 83 MPAs worldwide. Annual running costs per unit area spanned six orders of magnitude, and were higher in MPAs that were smaller, closer to coasts, and in high-cost, developed countries. Models extrapolating these findings suggest that a global MPA network meeting the World Parks Congress target of conserving 20–30% of the world’s seas might cost between 19 billion annually to run and would probably create around one million jobs. Although substantial, gross network costs are less than current government expenditures on harmful subsidies to industrial fisheries. They also ignore potential private gains from improved fisheries and tourism and are dwarfed by likely social gains from increasing the sustainability of fisheries and securing vital ecosystem services
Linear Operator Inequality and Null Controllability with Vanishing Energy for unbounded control systems
We consider linear systems on a separable Hilbert space , which are null
controllable at some time under the action of a point or boundary
control. Parabolic and hyperbolic control systems usually studied in
applications are special cases. To every initial state we
associate the minimal "energy" needed to transfer to in a time ("energy" of a control being the square of its norm). We
give both necessary and sufficient conditions under which the minimal energy
converges to for . This extends to boundary control
systems the concept of null controllability with vanishing energy introduced by
Priola and Zabczyk (Siam J. Control Optim. 42 (2003)) for distributed systems.
The proofs in Priola-Zabczyk paper depend on properties of the associated
Riccati equation, which are not available in the present, general setting. Here
we base our results on new properties of the quadratic regulator problem with
stability and the Linear Operator Inequality.Comment: In this version we have also added a section on examples and
applications of our main results. This version is similar to the one which
will be published on "SIAM Journal on Control and Optimization" (SIAM
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