470 research outputs found
Comparación de fórmulas chilenas e internacionales para valorar el arbolado urbano
Ponce-Donoso, M (reprint author), Univ Talca, Fac Ciencias Forestales, Casilla 747, Talca, Chile.The appraisal of urban trees is a practice adopted in diverse cities of world. This survey compared international formulae: Council of Tree Landscape Appraiser (CTLA), Burnley, Helliwell and Standard Tree Evaluation Method (STEM) and three Chilean methods applied in municipalities of Concepcion, La Pintana, Maip (COPIMA), Nunoa and Penalolen, in 14 different trees located in Talca city (Chile). The objective was to identify the differences and similarities of the monetary result in the application of these formulae, which was realized by a professional. These were analyzed using a non parametric variance test of Kruskal - Wallis and the multiple comparisons Duncan test. It was possible to determine that the Chilean formulae did not present statistically significant differences with the international formulae of Burnley and CTLA; whereas Penalolen and COPIMA formulae did not present any difference when contrasted with Helliwell. In addition, the STEM formula presented differences with all the Chilean analyzed formulae. In the valuation by tree, statistically significant differences were obtained, which showed the independence of the used formula. The exception was when being applied to emblematic species or to species that stand-out in some amenity. Likewise, it was observed that the basic value continues having a high impact in the appraisal final result and the use of the statistical test applied allows extending this type of analyses
Form factor for large quantum graphs: evaluating orbits with time-reversal
It has been shown that for a certain special type of quantum graphs the
random-matrix form factor can be recovered to at least third order in the
scaled time \tau using periodic-orbit theory. Two types of contributing pairs
of orbits were identified, those which require time-reversal symmetry and those
which do not. We present a new technique of dealing with contribution from the
former type of orbits.
The technique allows us to derive the third order term of the expansion for
general graphs. Although the derivation is rather technical, the advantages of
the technique are obvious: it makes the derivation tractable, it identifies
explicitly the orbit configurations which give the correct contribution, it is
more algorithmical and more system-independent, making possible future
applications of the technique to systems other than quantum graphs.Comment: 25 pages, 14 figures, accepted to Waves in Random Media (special
issue on Quantum Graphs and their Applications). Fixed typos, removed an
overly restrictive condition (appendix), shortened introductory section
Equilibrium statistical mechanics on correlated random graphs
Biological and social networks have recently attracted enormous attention
between physicists. Among several, two main aspects may be stressed: A non
trivial topology of the graph describing the mutual interactions between agents
exists and/or, typically, such interactions are essentially (weighted)
imitative. Despite such aspects are widely accepted and empirically confirmed,
the schemes currently exploited in order to generate the expected topology are
based on a-priori assumptions and in most cases still implement constant
intensities for links. Here we propose a simple shift in the definition of
patterns in an Hopfield model to convert frustration into dilution: By varying
the bias of the pattern distribution, the network topology -which is generated
by the reciprocal affinities among agents - crosses various well known regimes
(fully connected, linearly diverging connectivity, extreme dilution scenario,
no network), coupled with small world properties, which, in this context, are
emergent and no longer imposed a-priori. The model is investigated at first
focusing on these topological properties of the emergent network, then its
thermodynamics is analytically solved (at a replica symmetric level) by
extending the double stochastic stability technique, and presented together
with its fluctuation theory for a picture of criticality. At least at
equilibrium, dilution simply decreases the strength of the coupling felt by the
spins, but leaves the paramagnetic/ferromagnetic flavors unchanged. The main
difference with respect to previous investigations and a naive picture is that
within our approach replicas do not appear: instead of (multi)-overlaps as
order parameters, we introduce a class of magnetizations on all the possible
sub-graphs belonging to the main one investigated: As a consequence, for these
objects a closure for a self-consistent relation is achieved.Comment: 30 pages, 4 figure
How glassy are neural networks?
In this paper we continue our investigation on the high storage regime of a
neural network with Gaussian patterns. Through an exact mapping between its
partition function and one of a bipartite spin glass (whose parties consist of
Ising and Gaussian spins respectively), we give a complete control of the whole
annealed region. The strategy explored is based on an interpolation between the
bipartite system and two independent spin glasses built respectively by
dichotomic and Gaussian spins: Critical line, behavior of the principal
thermodynamic observables and their fluctuations as well as overlap
fluctuations are obtained and discussed. Then, we move further, extending such
an equivalence beyond the critical line, to explore the broken ergodicity phase
under the assumption of replica symmetry and we show that the quenched free
energy of this (analogical) Hopfield model can be described as a linear
combination of the two quenched spin-glass free energies even in the replica
symmetric framework
On composite systems of dilute and dense couplings
Composite systems, where couplings are of two types, a combination of strong
dilute and weak dense couplings of Ising spins, are examined through the
replica method. The dilute and dense parts are considered to have independent
canonical disordered or uniform bond distributions; mixing the models by
variation of a parameter alongside inverse temperature we
analyse the respective thermodynamic solutions. We describe the variation in
high temperature transitions as mixing occurs; in the vicinity of these
transitions we exactly analyse the competing effects of the dense and sparse
models. By using the replica symmetric ansatz and population dynamics we
described the low temperature behaviour of mixed systems.Comment: 35 pages, 9 figures, submitted to JPhys
From quantum graphs to quantum random walks
We give a short overview over recent developments on quantum graphs and
outline the connection between general quantum graphs and so-called quantum
random walks.Comment: 14 pages, 6 figure
Biodiesel synthesis: influence of alkaline catalysts in methanol-oil dispersion
CAPES - COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIORFAPERJ - FUNDAÇÃO DE AMPARO A PESQUISA DO ESTADO DO RIO DE JANEIROCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOBiodiesel synthesis from soybean oil using methanol and alkaline catalysts occurs in the following two consecutive steps: dispersion of methanol in the oil and methanolysis. The effect of the alkaline catalysts NaOCH3, KOCH3, NaOH, and KOH in the dispersi302342349CAPES - COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIORFAPERJ - FUNDAÇÃO DE AMPARO A PESQUISA DO ESTADO DO RIO DE JANEIROCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOCAPES - COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIORFAPERJ - FUNDAÇÃO DE AMPARO A PESQUISA DO ESTADO DO RIO DE JANEIROCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOsem informaçãosem informaçãosem informaçãoThe authors would like to thank CAPES, FAPERJ, and CNPq (Brazilian agencies) for their financial suppor
Q-dependence of the inelastic neutron scattering cross section for molecular spin clusters with high molecular symmetry
For powder samples of polynuclear metal complexes the dependence of the
inelastic neutron scattering intensity on the momentum transfer Q is known to
be described by a combination of so called interference terms. They reflect the
interplay between the geometrical structure of the compound and the spatial
properties of the wave functions involved in the transition. In this work, it
is shown that the Q-dependence is strongly interrelated with the molecular
symmetry of molecular nanomagnets, and, if the molecular symmetry is high
enough, is actually completely determined by it. A general formalism connecting
spatial symmetry and interference terms is developed. The arguments are
detailed for cyclic spin clusters, as experimentally realized by e.g. the
octanuclear molecular wheel Cr8, and the star like tetranuclear cluster Fe4.Comment: 8 pages, 1 figures, REVTEX
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