8,866 research outputs found
A thermodynamic counterpart of the Axelrod model of social influence: The one-dimensional case
We propose a thermodynamic version of the Axelrod model of social influence.
In one-dimensional (1D) lattices, the thermodynamic model becomes a coupled
Potts model with a bonding interaction that increases with the site matching
traits. We analytically calculate thermodynamic and critical properties for a
1D system and show that an order-disorder phase transition only occurs at T = 0
independent of the number of cultural traits q and features F. The 1D
thermodynamic Axelrod model belongs to the same universality class of the Ising
and Potts models, notwithstanding the increase of the internal dimension of the
local degree of freedom and the state-dependent bonding interaction. We suggest
a unifying proposal to compare exponents across different discrete 1D models.
The comparison with our Hamiltonian description reveals that in the
thermodynamic limit the original out-of-equilibrium 1D Axelrod model with noise
behaves like an ordinary thermodynamic 1D interacting particle system.Comment: 19 pages, 5 figure
A Unified Framework for Compositional Fitting of Active Appearance Models
Active Appearance Models (AAMs) are one of the most popular and
well-established techniques for modeling deformable objects in computer vision.
In this paper, we study the problem of fitting AAMs using Compositional
Gradient Descent (CGD) algorithms. We present a unified and complete view of
these algorithms and classify them with respect to three main characteristics:
i) cost function; ii) type of composition; and iii) optimization method.
Furthermore, we extend the previous view by: a) proposing a novel Bayesian cost
function that can be interpreted as a general probabilistic formulation of the
well-known project-out loss; b) introducing two new types of composition,
asymmetric and bidirectional, that combine the gradients of both image and
appearance model to derive better conver- gent and more robust CGD algorithms;
and c) providing new valuable insights into existent CGD algorithms by
reinterpreting them as direct applications of the Schur complement and the
Wiberg method. Finally, in order to encourage open research and facilitate
future comparisons with our work, we make the implementa- tion of the
algorithms studied in this paper publicly available as part of the Menpo
Project.Comment: 39 page
An Energy-conscious Transport Protocol for Multi-hop Wireless Networks
We present a transport protocol whose goal is to reduce power consumption without compromising delivery requirements of applications. To meet its goal of energy efficiency, our transport protocol (1) contains mechanisms to balance end-to-end vs. local retransmissions; (2) minimizes acknowledgment traffic using receiver regulated rate-based flow control combined with selected acknowledgements and in-network caching of packets; and (3) aggressively seeks to avoid any congestion-based packet loss. Within a recently developed ultra low-power multi-hop wireless network system, extensive simulations and experimental results demonstrate that our transport protocol meets its goal of preserving the energy efficiency of the underlying network.Defense Advanced Research Projects Agency (NBCHC050053
Detection of equine atypical myopathy-associated hypoglycin A in plant material: Optimisation and validation of a novel LC-MS based method without derivatisation
Hypoglycin A (HGA) toxicity, following ingestion of material from certain plants, is linked to an acquired multiple acyl-CoA dehydrogenase deficiency known as atypical myopathy, a commonly fatal form of equine rhabdomyolysis seen worldwide. Whilst some plants are known to contain this toxin, little is known about its function or the mechanisms that lead to varied HGA concentrations between plants. Consequently, reliable tools to detect this amino acid in plant samples are needed. Analytical methods for HGA detection have previously been validated for the food industry, however, these techniques rely on chemical derivatisation to obtain accurate results at low HGA concentrations. In this work, we describe and validate a novel method, without need for chemical derivatisation (accuracy = 84–94%; precision = 3–16%; reproducibility = 3–6%; mean linear range R2 = 0.999). The current limit of quantitation for HGA in plant material was halved (from 1μg/g in previous studies) to 0.5μg/g. The method was tested in Acer pseudoplatanus material and other tree and plant species. We confirm that A. pseudoplatanus is most likely the only source of HGA in trees found within European pastures
Magneto-Conductance Anisotropy and Interference Effects in Variable Range Hopping
We investigate the magneto-conductance (MC) anisotropy in the variable range
hopping regime, caused by quantum interference effects in three dimensions.
When no spin-orbit scattering is included, there is an increase in the
localization length (as in two dimensions), producing a large positive MC. By
contrast, with spin-orbit scattering present, there is no change in the
localization length, and only a small increase in the overall tunneling
amplitude. The numerical data for small magnetic fields , and hopping
lengths , can be collapsed by using scaling variables , and
in the perpendicular and parallel field orientations
respectively. This is in agreement with the flux through a `cigar'--shaped
region with a diffusive transverse dimension proportional to . If a
single hop dominates the conductivity of the sample, this leads to a
characteristic orientational `finger print' for the MC anisotropy. However, we
estimate that many hops contribute to conductivity of typical samples, and thus
averaging over critical hop orientations renders the bulk sample isotropic, as
seen experimentally. Anisotropy appears for thin films, when the length of the
hop is comparable to the thickness. The hops are then restricted to align with
the sample plane, leading to different MC behaviors parallel and perpendicular
to it, even after averaging over many hops. We predict the variations of such
anisotropy with both the hop size and the magnetic field strength. An
orientational bias produced by strong electric fields will also lead to MC
anisotropy.Comment: 24 pages, RevTex, 9 postscript figures uuencoded Submitted to PR
Quevedo y la ilustración de portadas: La vida de Marco Bruto y La caÃda para levantarse
Este trabajo presenta un estudio calcográfico de dos obras finales de Quevedo, las vidas de Marco Bruto y de San Pablo, que revela la promoción autorial sobre la invención de sus frontispicios, y apunta a una pasión poco transitada de su producción, con calidades inagotables para la comprensión discursiva. Quevedo no solo proporcionó el material arqueológico sobre el que se fundan las dos fachadas, sino que se congratuló de esa actividad inventiva. Ambos textos y sus portadas abren dimensiones inexploradas sobre el engarce quevediano de su ingenio plástico y discursivo, y sobre su afán coleccionista y ecléctico, facetas del escritor que solicitan estudio. De modo más concreto, también resaltan el brillo de su intuición simbólica, y su provecho hermenéutico de la imagen calcográfica, a través de la cual refuerza el rendimiento argumental de sus escritos. This is a study about the title pages of two final works by Quevedo; namely, the lives of Marco Bruto and San Pablo. Both works reveal the authorial promotion on the invention of both book fronts, and points out a scarcely analysed field of the author’s production which has fruitful implications on the understanding of his overall production. Quevedo did not only provided both title-pages with the archaeological material on which they are founded, but he too promoted himself for that invention. Both texts and their front pages open novel nuances about Quevedo’s combination of his discursive and plastic genius, and about his collector and eclectic spirit, decidedly, spheres of his creation which need revision. More specifically, they also underline his brilliant symbolic intuition and the peculiar profit that he attains of the engraved page, through which he wittily strengthens the line-plot of his writings
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