3,627 research outputs found
Scaling limit for a drainage network model
We consider the two dimensional version of a drainage network model
introduced by Gangopadhyay, Roy and Sarkar, and show that the appropriately
rescaled family of its paths converges in distribution to the Brownian web. We
do so by verifying the convergence criteria proposed by Fontes, Isopi, Newman
and Ravishankar.Comment: 15 page
Lyubeznik Ideals Minimally Generated by Four or Fewer Elements
Free resolutions for an ideal are constructions that tell us useful information about the structure of the ideal. Every ideal has one minimal free resolution which tells us significantly more about the structure of the ideal. In this thesis, we consider a specific type of resolution, the Lyubeznik resolution, for a monomial ideal I, which is constructed using a total order on the minimal generating set G(I). An ideal is called Lyubeznik if some total order on G(I) produces a minimal Lyubeznik resolution for I. We investigate the problem of characterizing whether an ideal I is Lyubeznik by using covers of generators of I, a construction due to Guo, Wu, and Yu [3] that is distinct from its Lyubeznik resolution. For monomial ideals of a polynomial ring, we characterize all Lyubeznik ideals that are minimally generated by four or fewer generators, and provide the total order that produces the minimal Lyubeznik resolution for all such ideals
Policies to Foster the Creation of Research-Based Spin-offs in Portugal
This paper presents a brief overview of the main government and institutional policies and mechanisms that promote and support (directly or indirectly) the creation of research-based spin-offs, as well as of the institutional changes that have been introduced to facilitate the commercial exploitation of results from academic research. In addition, there is an attempt to conduct a very preliminary assessment of some of the results achieved by these policies, within the limitations of the information available. It is concluded that the conditions for creating a firm that brings to the market knowledge or technology originating from academic research substantially improved in the last decade. Technology-based (and sometimes also scientific) entrepreneurship has been the object of several government policies and incentives and have also attracted the attention of other public and private actors, who launched a variety of programs to fund and otherwise support firm creation. This also coincided with institutional changes that facilitated the entrepreneurial initiatives of academic scientists. Although this appeared to have had positive effects in terms of the number of research-based spin-offs supported, the paper concludes, based on the limited data on results, that there is still work to do to improve the quality and effectiveness of the assistance provided. One step in this direction is a greater concentration and coordination of efforts.FC
Non-Equilibrium Modeling of the Fe XVII 3C/3D ratio for an Intense X-ray Free Electron Laser
We present a review of two methods used to model recent LCLS experimental
results for the 3C/3D line intensity ratio of Fe XVII (Bernitt et al. 2012),
the time-dependent collisional-radiative method and the density-matrix
approach. These are described and applied to a two-level atomic system excited
by an X-ray free electron laser. A range of pulse parameters is explored and
the effects on the predicted Fe XVII 3C and 3D line intensity ratio are
calculated. In order to investigate the behavior of the predicted line
intensity ratio, a particular pair of A-values for the 3C and 3D transitions
was chosen (2.22 10 s and 6.02 10
s for the 3C and 3D, respectively), but our conclusions are independent
of the precise values. We also reaffirm the conclusions from Oreshkina et
al.(2014, 2015): the non-linear effects in the density matrix are important and
the reduction in the Fe XVII 3C/3D line intensity ratio is sensitive to the
laser pulse parameters, namely pulse duration, pulse intensity, and laser
bandwidth. It is also shown that for both models the lowering of the 3C/3D line
intensity ratio below the expected time-independent oscillator strength ratio
has a significant contribution due to the emission from the plasma after the
laser pulse has left the plasma volume. Laser intensities above W/cm are required for a reduction in the 3C/3D line intensity
ratio below the expected time independent oscillator strength ratio
Contact process under renewals I
Motivated by questions regarding long range percolation, we investigate a
non-Markovian analogue of the Harris contact process in : an
individual is attached to each site , and it can be
infected or healthy; the infection propagates to healthy neighbors just as in
the usual contact process, according to independent exponential times with a
fixed rate ; nevertheless, the possible recovery times for an
individual are given by the points of a renewal process with heavy tail; the
renewal processes are assumed to be independent for different sites. We show
that the resulting processes have a critical value equal to zero.Comment: 13 page
Entry strategies in the face of incumbents dominant position: the case of advanced renewable energy technologies
The paper discusses the entry strategies adopted by research-based firms introducing
advanced renewable energy technologies in the electricity production sector, which
combines strong incumbent power with fast technological change. Drawing on
contributions from the literatures on sustainability transitions and on strategic
management of technology we build an analytical framework to address the conditions
faced by the new entrants and the attitude of established incumbents towards their
technologies. This framework is applied through in-depth case studies of new firms in
two energy fields that display different levels of technological maturity: wind and wave
energy. The paper presents preliminary results from a first set of case studies, which
provide some insights into the “commercialisation environment” prevailing in those
fields. They suggest that research-based firms tend to depend on the complementary
assets possessed by incumbents, but have conditions to protect their technologies; and
that the technology is relevant for (at least some) incumbents, which show interest on
them, or are directly involved in their development/use. This is, in most cases,
conducive to “cooperation” strategies, which assume different forms according to the
stage of development of the technology and its proximity to incumbent competences
and business modelsFCT
QREN – Operational Programme for Competitiveness Factors, the European Union – European Regional Development Fund and National Funds
Portuguese Foundation for Science and Technology under Project FCOMP-01-0124-FEDER-011377, Project PEst-C/EGE/UI4105/2011 and Project Project Pest-OE/EME/UI0252/2011
INESC Coimbr
Scaling Limit and Critical Exponents for Two-Dimensional Bootstrap Percolation
Consider a cellular automaton with state space
where the initial configuration is chosen according to a Bernoulli
product measure, 1's are stable, and 0's become 1's if they are surrounded by
at least three neighboring 1's. In this paper we show that the configuration
at time n converges exponentially fast to a final configuration
, and that the limiting measure corresponding to is in
the universality class of Bernoulli (independent) percolation.
More precisely, assuming the existence of the critical exponents ,
, and , and of the continuum scaling limit of crossing
probabilities for independent site percolation on the close-packed version of
(i.e., for independent -percolation on ), we
prove that the bootstrapped percolation model has the same scaling limit and
critical exponents.
This type of bootstrap percolation can be seen as a paradigm for a class of
cellular automata whose evolution is given, at each time step, by a monotonic
and nonessential enhancement.Comment: 15 page
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