5,878 research outputs found
Thresholds for macroparasite infections
We analyse here the equilibria of an infinite system of partial differential equations modelling the dynamics of a population infected by macroparasites. We find that it is possible to define a reproduction number R0 that satisfies the intuitive definition, and yields a sharp threshold in the behaviour of the system: when R0 1, the PFE is unstable and there exists a unique endemic equilibrium. The results mainly confirm what had been obtained in simplified models, except for the fact that no backwards bifurcation occur in this model. The stability of equilibria is established by extending an abstract linearization principle and by analysing the spectra of appropriate operators
On the convergence of the Fitness-Complexity Algorithm
We investigate the convergence properties of an algorithm which has been
recently proposed to measure the competitiveness of countries and the quality
of their exported products. These quantities are called respectively Fitness F
and Complexity Q. The algorithm was originally based on the adjacency matrix M
of the bipartite network connecting countries with the products they export,
but can be applied to any bipartite network. The structure of the adjacency
matrix turns to be essential to determine which countries and products converge
to non zero values of F and Q. Also the speed of convergence to zero depends on
the matrix structure. A major role is played by the shape of the ordered matrix
and, in particular, only those matrices whose diagonal does not cross the empty
part are guaranteed to have non zero values as outputs when the algorithm
reaches the fixed point. We prove this result analytically for simplified
structures of the matrix, and numerically for real cases. Finally, we propose
some practical indications to take into account our results when the algorithm
is applied.Comment: 13 pages, 8 figure
On Properties of Policy-Based Specifications
The advent of large-scale, complex computing systems has dramatically
increased the difficulties of securing accesses to systems' resources. To
ensure confidentiality and integrity, the exploitation of access control
mechanisms has thus become a crucial issue in the design of modern computing
systems. Among the different access control approaches proposed in the last
decades, the policy-based one permits to capture, by resorting to the concept
of attribute, all systems' security-relevant information and to be, at the same
time, sufficiently flexible and expressive to represent the other approaches.
In this paper, we move a step further to understand the effectiveness of
policy-based specifications by studying how they permit to enforce traditional
security properties. To support system designers in developing and maintaining
policy-based specifications, we formalise also some relevant properties
regarding the structure of policies. By means of a case study from the banking
domain, we present real instances of such properties and outline an approach
towards their automatised verification.Comment: In Proceedings WWV 2015, arXiv:1508.0338
The role of host population heterogeneity in the evolution of virulence
I examine here the effects of host heterogeneity in the growth of immune response on the evolution and co-evolution of virulence. The analysis is based on an extension of the 'nested model' by Gilchrist and Sasaki [Modeling host-parasite coevolution, J. Theor. Biol. 218 (2002), pp. 289-308]; the criteria for host and parasite evolution, in the paradigm of adaptive dynamics, for that model are derived in generality. Host heterogeneity is assumed to be fixed at birth according to a lognormal distribution or to the presence of two discrete types. In both cases, it is found that host heterogeneity determines a dramatic decrease in pathogen virulence, since pathogens will tune to the 'weakest' hosts. Finally we clarify how contrasting results present in the literature are due to different modelling assumptions
On a Formal and User-friendly Linguistic Approach to Access Control of Electronic Health Data
The importance of the exchange of Electronic Health Records (EHRs) between hospitals has been recognized by governments and institutions. Due to the sensitivity of data exchanged, only mature standards and implementations can be chosen to operate. This exchange process is of course under the control of the patient, who decides who has the rights to access her personal healthcare data and who has not, by giving her personal privacy consent. Patients’ privacy consent is regulated by local legislations, which can vary frequently from region to region. The technology implementing such privacy aspects must be highly adaptable, often resulting in complex security scenarios that cannot be easily managed by patients and software designers. To
overcome such security problems, we advocate the use of a linguistic approach that relies on languages for expressing policies with solid mathematical foundations. Our approach bases on FACPL, a policy language we have intentionally designed by taking inspiration from OASIS XACML, the de-facto standard used in all projects covering secure EHRs transmission protected by patients’ privacy consent. FACPL can express policies similar to those expressible by XACML but, differently from XACML, it has an intuitive syntax, a formal semantics and easy to use software tools supporting policy development and enforcement. In this paper, we
present the potentialities of our approach and outline ongoing work
The scientific influence of nations on global scientific and technological development
Determining how scientific achievements influence the subsequent process of
knowledge creation is a fundamental step in order to build a unified ecosystem
for studying the dynamics of innovation and competitiveness. Relying separately
on data about scientific production on one side, through bibliometric
indicators, and about technological advancements on the other side, through
patents statistics, gives only a limited insight on the key interplay between
science and technology which, as a matter of fact, move forward together within
the innovation space. In this paper, using citation data of both research
papers and patents, we quantify the direct influence of the scientific outputs
of nations on further advancements in science and on the introduction of new
technologies. Our analysis highlights the presence of geo-cultural clusters of
nations with similar innovation system features, and unveils the heterogeneous
coupled dynamics of scientific and technological advancements. This study
represents a step forward in the buildup of an inclusive framework for
knowledge creation and innovation
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