17,397 research outputs found
On the convergence to critical scaling profiles in submonolayer deposition models
In this work we study the rate of convergence to similarity profiles in a
mean field model for the deposition of a submonolayer of atoms in a crystal
facet, when there is a critical minimal size for the stability of the
formed clusters. The work complements recently published related results by the
same authors in which the rate of convergence was studied outside of a critical
direction in the cluster size vs. time plane. In this paper
we consider a different similarity variable, ,
corresponding to an inner expansion of that critical direction, and prove the
convergence of solutions to a similarity profile when with fixed, as well as the rate at which the limit is
approached.Comment: Dedicated to the memory of Jack Car
The Redner - Ben-Avraham - Kahng cluster system
We consider a coagulation model first introduced by Redner, Ben-Avraham and
Krapivsky in [Redner, Ben-Avraham, Kahng: Kinetics of 'cluster eating', J.
Phys. A: Math. Gen., 20 (1987), 1231-1238], the main feature of which is that
the reaction between a j-cluster and a k-cluster results in the creation of a
|j-k|-cluster, and not, as in Smoluchowski's model, of a (j+k)-cluster. In this
paper we prove existence and uniqueness of solutions under reasonably general
conditions on the coagulation coefficients, and we also establish
differenciability properties and continuous dependence of solutions. Some
interesting invariance properties are also proved. Finally, we study the
long-time behaviour of solutions, and also present a preliminary analysis of
their scaling behaviour.Comment: 24 pages. 2 figures. Dedicated to Carlos Rocha and Luis Magalhaes on
the occasion of their sixtieth birthday
Rates of convergence to scaling profiles in a submonolayer deposition model and the preservation of memory of the initial condition
We establish rates of convergence of solutions to scaling (or similarity)
profiles in a coagulation type system modelling submonolayer deposition. We
prove that, although all memory of the initial condition is lost in the
similarity limit, information about the large cluster tail of the initial
condition is preserved in the rate of approach to the similarity profile. The
proof relies in a change of variables that allows for the decoupling of the
original infinite system of ordinary differential equations into a closed
two-dimensional nonlinear system for the monomer--bulk dynamics and a lower
triangular infinite dimensional linear one for the cluster dynamics. The
detailed knowledge of the long time monomer concentration, which was obtained
earlier by Costin et al. in (O. Costin, M. Grinfeld, K.P. O'Neill and H. Park,
Long-time behaviour of point islands under fixed rate deposition, Commun. Inf.
Syst. 13, (2), (2013), pp.183-200) using asymptotic methods and is rederived
here by center manifold arguments, is then used for the asymptotic evaluation
of an integral representation formula for the concentration of -clusters.
The use of higher order expressions, both for the Stirling expansion and for
the monomer evolution at large times allow us to obtain, not only the
similarity limit, but also the rate at which it is approached.Comment: Revised according to referee's suggestions; to be published in SIAM
J. Math. Ana
Steps in modular specifications for concurrent modules
© 2015 Published by Elsevier B.V.The specification of a concurrent program module is a difficult problem. The specifications must be strong enough to enable reasoning about the intended clients without reference to the underlying module implementation. We survey a range of verification techniques for specifying concurrent modules, in particular highlighting four key concepts: auxiliary state, interference abstraction, resource ownership and atomicity. We show how these concepts combine to provide powerful approaches to specifying concurrent modules
The Redner - Ben-Avraham - Kahng coagulation system with constant coefficients: the finite dimensional case
We study the behaviour as of solutions to the
Redner--Ben-Avraham--Kahng coagulation system with positive and compactly
supported initial data, rigorously proving and slightly extending results
originally established in [4] by means of formal arguments.Comment: 13 pages, 1 figur
Social participation in the context of the urban public space renewal: the case of Lagarteiro neighborhood in Oporto
In 1980, Giancarlo de Carlo wrote in the Perspecta: Yale Journal, “An Architecture of the Participation”. Carlo, proposed a sequence of procedures: the problem definition, the solution and the results evaluation, in all the three steps, the social communities should be integrated in as part of a share and dynamic process. This text corresponds to a new way of understanding the importance of the social communities in the architecture definition. From de Carlo’s text, the main goal of this paper is to present the results of an intervention in public space renewal of the Lagarteiro neighborhood (in Oporto city) and the relation of this process with the participation of the resident population. The urban context of Lagarteiro’s neighborhood presented before the intervention the typical and classic signs of disqualification of environmental and urban peripheral areas of resettlement. The term “disadvantaged areas” is associated with these areas in urban or peri-urban case, was framed in a specific Portuguese policy, called Initiative Critical Neighborhoods. Being a recent intervention, the renewal of the public space in Lagarteiro is a complete case study that allows comprehending the participation phenomenon in nowadays, at the same time that seduces a reflexion about technical and architectural solutions for “critical” neighborhood.info:eu-repo/semantics/publishedVersio
Social housing policies in Portugal over the last 25 years: Three study cases
Theory of the Portuguese contemporary of architecture had based fundamental concepts on the answers given to the lacks verified in the 1970s when the Carnation Revolution (1974) happened. In those years, Housing subject was deeply debated among the architects, foreseeing the resolution of the dramatic situation of Portuguese society of that time.
After the SAAL program, launched in the revolutionary period, between 1974 and 1976, other programs were framed, giving continuity to the housing policies built under the democratic Constitution text (1976). This article focuses three study cases, presenting the architectural features that resulted from the applications three different political lines. The article aims at reflecting about a temporal arch of 25 years, analyzing as main cases, a new intervention in the outskirt of Lisbon located in Sargento Abílio neighbourhood, the renovation project of the Lagarteiro neighborhood built in the early 70s in the limits of Porto municipality, concluding with an intervention in the historical area of Porto in Tomás Gonzaga street, close to the borders defined by UNESCO as Humanity Heritage.info:eu-repo/semantics/publishedVersio
A phenomenological model for magnetoresistance in granular polycrystalline colossal magnetoresistive materials: the role of spin polarised tunnelling at the grain boundaries
It has been observed that in bulk and polycrystalline thin films of collossal
magnetoresistive (CMR) materials the magnetoresistance follows a different
behaviour compared to single crystals or single crystalline films below the
ferromagnetic transition temperature Tc. In this paper we develop a
phenomenological model to explain the magnetic field dependence of resistance
in granular CMR materials taking into account the spin polarised tunnelling at
the grain boundaries. The model has been fitted to two systems, namely,
La0.55Ho0.15Sr0.3MnO3 and La1.8Y0.5Ca0.7Mn2O7. From the fitted result we have
separated out, in La0.55Ho0.15Sr0.3MnO3, the intrinsic contribution from the
intergranular contribution to the magnetoresistance coming from spin polarised
tunnelling at the grain boundaries. It is observed that the temperature
dependence of the intrinsic contribution to the magnetoresistance in
La0.55Ho0.15Sr0.3MnO3 follows the prediction of double exchange model for all
values of field.Comment: 14 pages + 5 figures, postscript (to appear in Journal of Applied
Physics
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